Bimesogenic compounds and mesogenic media

ABSTRACT

The invention relates to bimesogenic compounds of formula I 
                         
wherein R 11 , R 12 , MG 11 , MG 12 , X 11 , X 12  and Sp 1  have the meaning given in claim  1 , to the use of bimesogenic compounds of formula l in liquid crystal media and particular to flexoelectric liquid crystal devices comprising a liquid crystal medium according to the present invention.

The invention relates to bimesogenic compounds of formula I

wherein R¹¹, R¹², MG¹¹, MG¹² and Sp¹ have the meaning given hereinbelow, to the use of bimesogenic compounds of formula I in liquidcrystal media and particular to flexoelectric liquid crystal devicescomprising a liquid crystal medium according to the present invention.

Liquid Crystal Displays (LCDs) are widely used to display information.LCDs are used for direct view displays, as well as for projection typedisplays. The electro-optical mode which is employed for most displaysstill is the twisted nematic (TN)-mode with its various modifications.Besides this mode, the super twisted nematic (STN)-mode and morerecently the optically compensated bend (OCB)-mode and the electricallycontrolled birefringence (ECB)-mode with their various modifications, ase. g. the vertically aligned nematic (VAN), the patterned ITO verticallyaligned nematic (PVA)-, the polymer stabilized vertically alignednematic (PSVA)-mode and the multi domain vertically aligned nematic(MVA)-mode, as well as others, have been increasingly used. All thesemodes use an electrical field, which is substantially perpendicular tothe substrates, respectively to the liquid crystal layer. Besides thesemodes there are also electro-optical modes employing an electrical fieldsubstantially parallel to the substrates, respectively the liquidcrystal layer, like e.g. the In Plane Switching (short IPS) mode (asdisclosed e.g. in DE 40 00 451 and EP 0 588 568) and the Fringe FieldSwitching (FFS) mode. Especially the latter mentioned electro-opticalmodes, which have good viewing angle properties and improved responsetimes, are increasingly used for LCDs for modern desktop monitors andeven for displays for TV and for multimedia applications and thus arecompeting with the TN-LCDs.

Further to these displays, new display modes using cholesteric liquidcrystals having a relatively short cholesteric pitch have been proposedfor use in displays exploiting the so called “flexo-electric” effect.The term “liquid crystal”, “mesomorphic compound” or “mesogeniccompound” (also shortly referred to as “mesogen”) means a compound thatunder suitable conditions of temperature, pressure and concentration canexist as a mesophase (nematic, smectic, etc.) or in particular as a LCphase. Non-amphiphilic mesogenic compounds comprise for example one ormore calamitic, banana-shaped or discotic mesogenic groups.

Flexoelectric liquid crystal materials are known in prior art. Theflexoelectric effect is described inter alia by Chandrasekhar, “LiquidCrystals”, 2nd edition, Cambridge University Press (1992) and P. G.deGennes et al., “The Physics of Liquid Crystals”, 2nd edition, OxfordScience Publications (1995).

Derivatives of 1,1-diphenylethylene and naphthalene are disclosed byAshley, J. N., Grove, J. F., and Henshall, T., “Attempts to find newChemotherapeutic Amides. Part IX. Derivatives of 1:1-Diphenyl-ethyleneand Naphthalene. Journal of the Chemical Society, (1948), pages 261-264.

Already GB 2356629 discloses bimesogenic compounds and their use inflexoelectric devices.

Dimeric materials linked by alkyl chains showing a new nematic phasehave been disclosed by Tamba, M.-G., Lewis, R. A., Kohlmeier, A., andMehl, G. H., in “Nematic—nematic phase transitions in liquid crystaldimmers with a negative dielectric anisotropy” poster presentation atthe ILCC 2010 and Tamba, M.-G., Kohlmeier, A., Lewis, R. A., and Mehl,G. H., in “Nematic—nematic phase transitions in dimmers, the results ofcalorimetric, optical and structural investigations” poster presentationat the ILCC 2010.

WO 2013/004333 also discloses bimesogenic materials comprising alkylenespacers showing a second nematic phase.

In these displays the cholesteric liquid crystals are oriented in the“uniformly lying helix” arrangement (ULH), which also give this displaymode its name. For this purpose, a chiral substance which is mixed witha nematic material induces a helical twist transforming the materialinto a chiral nematic material, which is equivalent to a cholestericmaterial. The term “chiral” in general is used to describe an objectthat is non-superimposable on its mirror image. “Achiral” (non-chiral)objects are objects that are identical to their mirror image. The termschiral nematic and cholesteric are used synonymously in thisapplication, unless explicitly stated otherwise. The pitch induced bythe chiral substance (P₀) is in a first approximation inverselyproportional to the concentration (c) of the chiral material used. Theconstant of proportionality of this relation is called the helicaltwisting power (HTP) of the chiral substance and defined by equation (1)HTP≡1/(c·P ₀)  (1)wherein

-   c is concentration of the chiral compound.

The uniform lying helix texture is realized using a chiral nematicliquid crystal with a short pitch, typically in the range from 0.2 μm to1 μm, preferably of 1.0 μm or less, in particular of 0.5 μm or less,which is unidirectional aligned with its helical axis parallel to thesubstrates, e.g. glass plates, of a liquid crystal cell. In thisconfiguration the helical axis of the chiral nematic liquid crystal isequivalent to the optical axis of a birefringent plate.

If an electrical field is applied to this configuration normal to thehelical axis the optical axis is rotated in the plane of the cell,similar as the director of a ferroelectric liquid crystal rotate as in asurface stabilized ferroelectric liquid crystal display. Theflexoelectric effect is characterized by fast response times typicallyranging from 6 μs to 100 μs. It further features excellent grey scalecapability.

The field induces a splay bend structure in the director which isaccommodated by a tilt in the optical axis. The angle of the rotation ofthe axis is in first approximation directly and linearly proportional tothe strength of the electrical field. The optical effect is best seenwhen the liquid crystal cell is placed between crossed polarizers withthe optical axis in the unpowered state at an angle of 22.5° to theabsorption axis of one of the polarizers. This angle of 22.5° is alsothe ideal angle of rotation of the electric field, as thus, by theinversion the electrical field, the optical axis is rotated by 45° andby appropriate selection of the relative orientations of the preferreddirection of the axis of the helix, the absorption axis of the polarizerand the direction of the electric field, the optical axis can beswitched from parallel to one polarizer to the center angle between bothpolarizers. The optimum contrast is then achieved when the total angleof the switching of the optical axis is 45°. In that case thearrangement can be used as a switchable quarter wave plate, provided theoptical retardation, i. e. the product of the effective birefringence ofthe liquid crystal and the cell gap, is selected to be the quarter ofthe wave length. In this context the wavelength referred to is 550 nm,the wavelength for which the sensitivity of the human eye is highest,unless explicitly stated otherwise.

The angle of rotation of the optical axis (Φ) is given in goodapproximation by formula (2)tan Φ=ēP ₀ E/(2πK)  (2)wherein

-   P₀ is the undisturbed pitch of the cholesteric liquid crystal,-   ē is the average [ē=½(e_(splay)+e_(bend))] of the splay    flexoelectric coefficient (e_(splay)) and the bend flexoelectric    coefficient (e_(bend)),-   E is the electrical field strength and-   K is the average [K=½ (k₁₁+k₃₃)] of the splay elastic constant (k₁₁)    and the bend elastic constant (K₃₃)    and wherein-   ē/K is called the flexo-elastic ratio.

This angle of rotation is half the switching angle in a flexoelectricswitching element.

The response time (τ) of this electro-optical effect is given in goodapproximation by formula (3)τ=[P ₀/(2π)]² ·γ/K  (3)wherein

-   γ is the effective viscosity coefficient associated with the    distortion of the helix.

There is a critical field (E_(c)) to unwind the helix, which can beobtained from equation (4)E _(c)=(π² /P ₀)·[k ₂₂/(ε₀·Δε)]^(1/2)  (4)wherein

-   k₂₂ is the twist elastic constant,-   ε₀ is the permittivity of vacuum and-   Δε is the dielectric anisotropy of the liquid crystal.

In this mode, however several problems still have to be resolved, whichare, amongst others, difficulties in obtaining the required uniformorientation, an unfavorably high voltage required for addressing, whichis incompatible with common driving electronics, a not really dark “offstate”, which deteriorates the contrast, and, last not least, apronounced hysteresis in the electro-optical characteristics.

A relatively new display mode, the so-called uniformly standing helix(USH) mode, may be considered as an alternative mode to succeed the IPS,as it can show improved black levels, even compared to other displaymode providing wide viewing angles (e.g. IPS, VA etc.).

For the USH mode, like for the ULH mode, flexoelectric switching hasbeen proposed, using bimesogenic liquid crystal materials. Bimesogeniccompounds are known in general from prior art (cf. also Hori, K.,Iimuro, M., Nakao, A., Toriumi, H., J. Mol. Struc. 2004, 699, 23-29).The term “bimesogenic compound” relates to compounds comprising twomesogenic groups in the molecule. Just like normal mesogens they canform many mesophases, depending on their structure. In particularcompounds of formula I induce a second nematic phase, when added to anematic liquid crystal medium.

The term “mesogenic group” means in this context, a group with theability to induce liquid crystal (LC) phase behaviour. The compoundscomprising mesogenic groups do not necessarily have to exhibit an LCphase themselves. It is also possible that they show LC phase behaviouronly in mixtures with other compounds. For the sake of simplicity, theterm “liquid crystal” is used hereinafter for both mesogenic and LCmaterials.

However, due to the unfavorably high driving voltage required, to therelatively narrow phase range of the chiral nematic materials and totheir irreversible switching properties, materials from prior art arenot compatible for the use with current LCD driving schemes.

For displays of the USH and ULH mode, new liquid crystalline media withimproved properties are required. Especially the birefringence (Δn)should be optimized for the optical mode. The birefringence Δn herein isdefined in equation (5)Δn=n _(e) −n _(o)  (5)wherein n_(e) is the extraordinary refractive index and n_(o) is theordinary refractive index, and the average refractive index n_(av). isgiven by the following equation (6).n _(av).=[(2n _(o) ² +n _(e) ²)/3]^(1/2)  (6)

The extraordinary refractive index n_(e) and the ordinary refractiveindex n_(o) can be measured using an Abbe refractometer. Δn can then becalculated from equation (5).

Furthermore, for displays utilizing the USH or ULH mode the opticalretardation d*Δn (effective) of the liquid crystal media shouldpreferably be such that the equation (7)sin 2(π·d·Δn/λ)=1  (7)wherein

-   d is the cell gap and-   λ is the wave length of light-   is satisfied. The allowance of deviation for the right hand side of    equation (7) is +/−3%.

The wave length of light generally referred to in this application is550 nm, unless explicitly specified otherwise.

The cell gap of the cells preferably is in the range from 1 μm to 20 μm,in particular within the range from 2.0 μm to 10 μm.

For the ULH/USH mode, the dielectric anisotropy (Δε) should be as smallas possible, to prevent unwinding of the helix upon application of theaddressing voltage. Preferably Δε should be slightly higher than 0 andvery preferably be 0.1 or more, but preferably 10 or less, morepreferably 7 or less and most preferably 5 or less. In the presentapplication the term “dielectrically positive” is used for compounds orcomponents with Δε>3.0, “dielectrically neutral” with −1.5≤Δε≤3.0 and“dielectrically negative” with Δε<−1.5. Δε is determined at a frequencyof 1 kHz and at 20° C. The dielectric anisotropy of the respectivecompound is determined from the results of a solution of 10% of therespective individual compound in a nematic host mixture. In case thesolubility of the respective compound in the host medium is less than10% its concentration is reduced by a factor of 2 until the resultantmedium is stable enough at least to allow the determination of itsproperties. Preferably the concentration is kept at least at 5%,however, in order to keep the significance of the results a high aspossible. The capacitance of the test mixtures are determined both in acell with homeotropic and with homogeneous alignment. The cell gap ofboth types of cells is approximately 20 μm. The voltage applied is arectangular wave with a frequency of 1 kHz and a root mean square valuetypically of 0.5 V to 1.0 V, however, it is always selected to be belowthe capacitive threshold of the respective test mixture.

Δε is defined as (ε_(∥)−ε_(⊥)), whereas ε_(av). is (ε_(∥)+2ε_(⊥))/3. Thedielectric permittivity of the compounds is determined from the changeof the respective values of a host medium upon addition of the compoundsof interest. The values are extrapolated to a concentration of thecompounds of interest of 100%. A typical The host mixture is disclosedin H. J. Coles et al., J. Appl. Phys. 2006, 99, 034104 and has thecomposition given in the table.

TABLE 1 Host mixture composition Compound ConcentrationF-PGI-ZI-9-Z-GP-F 25% F-PGI-ZI-11-Z-GP-F 25% F-PGI-O-5-O-PP-N 9.5% F-PGI-O-7-O-PP-N 39% CD-1 1.5% 

Besides the above mentioned parameters, the media have to exhibit asuitably wide range of the nematic phase, a rather small rotationalviscosity and an at least moderately high specific resistivity.

Similar liquid crystal compositions with short cholesteric pitch forflexoelectric devices are known from EP 0 971 016, GB 2 356 629 andColes, H. J., Musgrave, B., Coles, M. J., and Willmott, J., J. Mater.Chem., 11, p. 2709-2716 (2001). EP 0 971 016 reports on mesogenicestradiols, which, as such, have a high flexoelectric coefficient. GB 2356 629 suggests the use of bimesogenic compounds in flexoelectricdevices. The flexoelectric effect herein has been investigated in purecholesteric liquid crystal compounds and in mixtures of homologouscompounds only so far. Most of these compounds were used in binarymixtures consisting of a chiral additive and a nematic liquid crystalmaterial being either a simple, conventional monomesogenic material or abimesogenic one. These materials do have several drawbacks for practicalapplications, like insufficiently wide temperature ranges of the chiralnematic—or cholesteric phase, too small flexoelectric ratios, smallangles of rotation.

One aim of the invention was to provide improved flexoelectric devicesthat exhibit high switching angles and fast response times. Another aimwas to provide liquid crystal materials with advantageous properties, inparticular for use in flexoelectric displays that enable good uniformalignment over the entire area of the display cell without the use of amechanical shearing process, good contrast, high switching angles andfast response times also at low temperatures. The liquid crystalmaterials should exhibit low melting points, broad chiral nematic phaseranges, short temperature independent pitch lengths and highflexoelectric coefficients. Other aims of the present invention areimmediately evident to the person skilled in the art from the followingdetailed description.

The inventors have found out that the above aims can be surprisinglyachieved by providing bimesogenic compounds according to the presentinvention. These compounds, when used in chiral nematic liquid crystalmixtures, lead to low melting points, broad chiral nematic phases. Inparticular, they exhibit relatively high values of the elastic constantk₁₁, low values of the bend elastic constant k₃₃ and the flexoelectriccoefficient.

Thus, the present invention relates to bimesogenic compounds of formulaI

wherein

-   R¹¹ and R¹² are each independently H, halogen, preferably F or Cl,    CN, NO₂ or a straight-chain or branched alkyl group with 1 to 25 C    atoms which may be unsubstituted, mono- or polysubstituted by    halogen or CN, it being also possible for one or more non-adjacent    CH₂ groups to be replaced, in each occurrence independently from one    another, by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —O—CO—O—,    —S—CO—, —CO—S—, —CH═CH—, —CH═CF—, —CF═CF— or —C≡C— in such a manner    that oxygen atoms are not linked directly to one another, preferably    a polar group, more preferably F, Cl, CN, OCF₃, CF₃,-   MG¹¹ and MG¹² are each independently a mesogenic group,    at least one of-   MG¹¹ and MG¹² is a mesogenic group, where MG¹¹ or MG¹² contains at    least one fused ring group selected from alicyclic, aromatic and    condensed groups made up of 7 to 23 carbon atoms, wherein one or two    non-adjacent CH groups each may be replaced by an N-atom and/or one    or two non-adjacent CH₂ groups, independently of each other, may be    replaced by an O- or an S-atom, and which optionally is substituted    by one or more halogen atoms, preferably F and/or Cl, and/or by one    or more alkyl group(s) each independently having 1 to 9 C atoms,    preferably by one alkyl group having 1 to 9 C atoms and/or by one    more alkoxy group(s) each independently having 1 to 9 C atoms,    wherein the mesogenic group can also contain 0 to 3, preferably 0, 1    or 2, more preferably 0 or 1, six membered rings selected from    1,4-phenylene, wherein in addition one or more CH groups may be    replaced by N, trans-1,4-cyclo-hexylene in which, in addition, one    or two non-adjacent CH₂ groups may be replaced by O and/or S,    1,4-cyclohexenylene, 1,4-bicyclo-(2,2,2)-octylene,    piperidine-1,4-diyl, naphthalene-2,6-diyl,    decahydro-naphthalene-2,6-diyl,    1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl,    spiro[3.3]heptane-2,6-diyl or dispiro[3.1.3.1] decane-2,8-diyl, it    being possible for all these groups to be unsubstituted, mono-, di-,    tri- or tetrasubstituted with F, Cl, CN or alkyl, alkenyl, alkoxy,    alkenyloxy, alkylcarbonyl or alkoxycarbonyl groups, preferably    alkyl, alkoxy, alkenyl alkylcarbonyl or alkoxycarbonyl groups    preferably with 1 to 15, preferably 1 to 7 C atoms, wherein one or    more H atoms may be substituted by F or Cl,-   Sp¹ is a spacer group comprising 1, 3 or 5 to 40 C atoms, wherein    one or more non-adjacent and non-terminal CH₂ groups may also be    replaced by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —O—CO—, —S—CO—, —O—COO—,    —CO—S—, —CO—O—, —CH(halogen)-, —CH(CN)—, —CH═CH— or —C≡C—, however    in such a way that no two O-atoms are adjacent to one another, now    two —CH═CH— groups are adjacent to each other and no two groups    selected from —O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O— and —CH═CH—    are adjacent to each other, preferably (—CH₂)_(n)—(i.e. 1,n-alkylene    with n C atoms), with n an integer, preferably from 3 to 19, more    preferably from 3 to 11, most preferably an odd integer (i.e. 3, 5,    7, 9 or 11),-   X¹¹ and X¹² are independently from one another a linking group    selected from —CO—, —CO—O—, —O—CO—, —O—, —CH═CH—, —C≡C—, —CO—S—,    —S—CO—, —CS—S—, —S—, —CF₂—, —CF₂—O—, —O—CF₂— and a single bond,    preferably —CO—O—, —O—CO— or a single bond, most preferably a single    bond,    however under the condition that in —X¹¹-Sp¹-X¹²— no two O-atoms are    adjacent to one another, now two —CH═CH— groups are adjacent to each    other and no two groups selected from —O—CO—, —S—CO—, —O—CO—O—,    —CO—S—, —CO—O—, —CF₂—O—, —O—CF₂— and —CH═CH— are adjacent to each    other.

In a first preferred embodiment

-   X¹¹ and X¹² are different from each another and otherwise    independently from one another are a linking group as defined above,    preferably selected from —CO—O—, —O—CO—, —CF₂—, —CF₂—O—, —O—CF₂—,    —CH═CH—, —C≡C—, —O—, —S—CO—, —CO—S—, —S— and —CO—, or a single bond,    preferably X¹¹ is —CO—O— or —O— and X¹² is a single bond or X¹¹ is    —CO—O— and X¹² is —O—, most preferably X¹¹ is —CO—O— and X¹² is a    single bond.

In a further preferred embodiment, which may be different from oridentical with any of the preferred embodiments,

-   X¹² independently from X¹¹ has one of the meanings given for X¹¹ or    is a linking group selected from —CO—O—, —O—CO—, —CH═CH—, —C≡C— and    —O— or a single bond.

In a further preferred embodiment, which may be different from oridentical with any of the preferred embodiments, the mesogenic groupsMG¹¹ and MG¹² are non-symmetric to each other.

Preferred compounds of formula I are compounds, in which

-   MG¹¹ and MG¹² are independently from one another a group of    (partial) formula II    -A¹¹-(Z¹¹-A¹²)_(k)-  II    wherein-   Z¹¹ are, independently of each other in each occurrence, a single    bond or a spacer group, preferably selected from —COO—, —OCO—,    —O—CO—O—, —OCH₂—, —CH₂O—, —OCF₂—, —CF₂O—, —CH₂CH₂—, —(CH₂)₄—,    —CF₂CF₂—, —CH═CH—, —CF═CF—, —CH═CH—COO—, —OCO—CH═CH— and —C≡C—,    optionally substituted with one or more of F, S and/or Si,    preferably a single bond,    one or more of-   A¹¹ and A¹² contains or is at least one fused ring group selected    from alicyclic, aromatic and condensed groups made up of 7 to 23    carbon atoms, wherein one or two non-adjacent CH groups each may be    replaced by an N-atom and/or one or two non-adjacent CH₂ groups,    independently of each other, may be replaced by an O- or an S-atom,    and which optionally is substituted by one or more halogen atoms,    preferably F and/or Cl, and/or by one or more alkyl group(s) each    independently having 1 to 9 C atoms, preferably by one alkyl group    having 1 to 9 C atoms,    and the other-   A¹¹ and A¹² are each independently in each occurrence 1,4-phenylene,    wherein in addition one or more CH groups may be replaced by N,    trans-1,4-cyclo-hexylene in which, in addition, one or two    non-adjacent CH₂ groups may be replaced by O and/or S,    1,4-cyclohexenylene, 1,4-bicyclo-(2,2,2)-octylene,    piperidine-1,4-diyl, naphthalene-2,6-diyl,    decahydro-naphthalene-2,6-diyl,    1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl, it    being possible for all these groups to be unsubstituted, mono-, di-,    tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy,    alkylcarbonyl or alkoxycarbonyl groups with 1 to 7 C atoms, wherein    one or more H atoms may be substituted by F or Cl, preferably F, Cl,    CH₃ or CF₃, and-   k is 0, 1, 2, 3 or 4, preferably 1, 2 or 3 and, most preferably 1 or    2.

Especially preferred compounds of formula I, in which MG¹¹ and MG¹² aredifferent from one another.

Preferably this fused ring group, respectively these fused ring groups,are independently of each other selected from the following group ofpartial formulae

wherein preferably

-   L in each occurrence independently of each other is F or Cl,    preferably F, and-   r is 0, 1, 2 or 3, preferably 0, 1 or 2-   i is 0, 1 or 2, preferably 0 or 1, and-   j is 0 or 1, preferably 0.

A smaller group of preferred mesogenic groups of formula II comprisingonly 6-membered rings is listed below. For reasons of simplicity, Phe inthese groups is 1,4-phenylene, PheL is a 1,4-phenylene group which issubstituted by 1 to 4 groups L, with L being preferably F, Cl, CN, OH,NO₂ or an optionally fluorinated alkyl, alkoxy or alkanoyl group with 1to 7 C atoms, very preferably F, Cl, CN, OH, NO₂, CH₃, C₂H₅, OCH₃,OC₂H₅, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, OCF₃, OCHF₂, OC₂F₅, inparticular F, Cl, CN, CH₃, C₂H₅, OCH₃, COCH₃ and OCF₃, most preferablyF, Cl, CH₃, OCH₃ and COCH₃ and Cyc is 1,4-cyclohexylene. This listcomprises the sub-formulae shown below as well as their mirror images-Phe-Z-Phe-  II-1-Phe-Z-Cyc-  II-2-Cyc-Z-Cyc-  II-3-Phe-Z-PheL-  II-4-PheL-Z-Phe-  II-5-PheL-Z-Cyc-  II-6-PheL-Z-PheL-  II-7-Phe-Z-Phe-Z-Phe-  II-8-Phe-Z-Phe-Z-Cyc-  II-9-Phe-Z-Cyc-Z-Phe-  II-10-Cyc-Z-Phe-Z-Cyc-  II-11-Phe-Z-Cyc-Z-Cyc-  II-12-Cyc-Z-Cyc-Z-Cyc-  II-13-Phe-Z-Phe-Z-PheL-  II-14-Phe-Z-PheL-Z-Phe-  II-15-PheL-Z-Phe-Z-Phe-  II-16-PheL-Z-Phe-Z-PheL-  II-17-PheL-Z-PheL-Z-Phe-  II-18-PheL-Z-PheL-Z-PheL-  II-19-Phe-Z-PheL-Z-Cyc-  II-20-Phe-Z-Cyc-Z-PheL-  II-21-Cyc-Z-Phe-Z-PheL-  II-22-PheL-Z-Cyc-Z-PheL-  II-23-PheL-Z-PheL-Z-Cyc-  II-24-PheL-Z-Cyc-Z-Cyc-  II-25-Cyc-Z-PheL-Z-Cyc-  II-26-Phe-Z-Phe-Phe-  II-27-Phe-Phe-Z-Cyc-  II-28wherein

-   Cyc is 1,4-cyclohexlene, preferably trans-1,4-cyclohexlene,-   Phe is 1,4-phenylene,-   PheL is 1,4-phenylene, which is substituted by one, two or three    fluorine atoms, by one or two Cl atoms or by one Cl atom and one F    atom, and-   Z has one of the meanings of Z¹¹ as given under partial formula II,    at least one is preferably selected from —COO—, —OCO—, —O—CO—O—,    —OCH₂—, —CH₂O—, —OCF₂— or —CF₂O—.

Particularly preferred are the sub-formulae II-1, II-4, II-5, II-7 andII-27

In these preferred groups Z in each case independently has one of themeanings of Z¹¹ as given under formula I. Preferably one of Z is —COO—,—OCO—, —CH₂—O—, —O—CH₂—, —CF₂—O— or —O—CF₂—, more preferably —COO—,—O—CH₂— or —CF₂—O—, and the others preferably are a single bond.

Very preferably at least one of the mesogenic groups MG¹¹ and MG¹² is,and preferably both of them are each and independently, selected fromthe following formulae IIa to IIn (the two reference Nos. “II i” and “IIl” being deliberately omitted to avoid any confusion) and their mirrorimages

wherein

-   L is in each occurrence independently of each other F or Cl,    preferably F and-   r is in each occurrence independently of each other 0, 1, 2 or 3,    preferably 0, 1 or 2.

The group

in these preferred formulae is very preferably denoting

furthermore

L is in each occurrence independently of each other F or Cl, F.

In case of compounds with a unpolar group, R¹¹ and R¹² are preferablyalkyl with up to 15 C atoms or alkoxy with 2 to 15 C atoms.

If R¹¹ or R¹² is an alkyl or alkoxy radical, i.e. where the terminal CH₂group is replaced by —O—, this may be straight-chain or branched. It ispreferably straight-chain, has 2, 3, 4, 5, 6, 7 or 8 carbon atoms andaccordingly is preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl,octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy or octoxy,furthermore methyl, nonyl, decyl, undecyl, dodecyl, tridecyl,tetradecyl, pentadecyl, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy ortetradecoxy, for example.

Oxaalkyl, i.e. where one CH₂ group is replaced by —O—, is preferablystraight-chain 2-oxapropyl (=methoxymethyl), 2-(=ethoxymethyl) or3-oxabutyl (=2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-,7-, 8- or 9-oxadecyl, for example.

In case of a compounds with a terminal polar group, R¹¹ and R¹² areselected from CN, NO₂, halogen, OCH₃, OCN, SCN, COR^(x), COOR^(x) or amono- oligo- or polyfluorinated alkyl or alkoxy group with 1 to 4 Catoms. R^(x) is optionally fluorinated alkyl with 1 to 4, preferably 1to 3 C atoms. Halogen is preferably F or Cl.

Especially preferably R¹¹ and R¹² in formula I are selected of H, F, Cl,CN, NO₂, OCH₃, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, C₂F₅, OCF₃, OCHF₂,and OC₂F₅, in particular of H, F, Cl, CN, OCH₃ and OCF₃, especially ofH, F, CN and OCF₃.

In addition, compounds of formula I containing an achiral branched groupR¹¹ and/or R¹² may occasionally be of importance, for example, due to areduction in the tendency towards crystallisation. Branched groups ofthis type generally do not contain more than one chain branch. Preferredachiral branched groups are isopropyl, isobutyl (=methylpropyl),isopentyl (=3-methylbutyl), isopropoxy, 2-methyl-propoxy and3-methylbutoxy.

The spacer group Sp¹ is preferably a linear or branched alkylene grouphaving 1, 3 or 5 to 40 C atoms, in particular 1, 3 or 5 to 25 C atoms,very preferably 1, 3 or 5 to 15 C atoms, and most preferably 5 to 15 Catoms, in which, in addition, one or more non-adjacent and non-terminalCH₂ groups may be replaced by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —O—CO—,—S—CO—, —O—COO—, —CO—S—, —CO—O—, —CH(halogen)-, —CH(CN)—, —CH═CH— or—C≡C—.

“Terminal” CH₂ groups are those directly bonded to the mesogenic groups.

Accordingly, “non-terminal” CH₂ groups are not directly bonded to themesogenic groups MG¹¹ and MG¹².

Typical spacer groups are for example —(CH₂)_(o)—,—(CH₂CH₂O)_(p)—CH₂CH₂—, with o being an integer from 5 to 40, inparticular from 5 to 25, very preferably from 5 to 15, and p being aninteger from 1 to 8, in particular 1, 2, 3 or 4.

Preferred spacer groups are pentylene, hexylene, heptylene, octylene,nonylene, decylene, undecylene, dodecylene, octadecylene,diethyleneoxyethylene, dimethyleneoxybutylene, pentenylene, heptenylene,nonenylene and undecenylene, for example.

Especially preferred are inventive compounds of formula I wherein Sp isdenoting alkylene with 5 to 15 C atoms. Straight-chain alkylene groupsare especially preferred.

Preferred are spacer groups, which are straight-chain alkylene with oddnumbers of C atoms, preferably a having 5, 7, 9, 11, 13 or 15 C atoms,very preferred are straight-chain alkylene spacers having 7, 9, and 11 Catoms.

In another embodiment of the present invention the spacer groups arestraight-chain alkylenes with even numbers of C atoms, preferably having6, 8, 10, 12 and 14 C atoms. This embodiment is particularly preferredif one of X¹¹ and X¹² consists of one atom, i.e. is —S— or —O—, or ofthree atoms, e.g. is —S—CO—, —S—CO—S— or —S—CS—S—, and the other doesnot consist of one or three C atoms.

Especially preferred are inventive compounds of formula I wherein Sp isdenoting complete deuterated alkylene with 5 to 15 C atoms. Verypreferred are deuterated straight-chain alkylene groups. Most preferredare partially deuterated straight-chain alkylene groups.

Preferred are compounds of formula I wherein the mesogenic groupsR¹¹-MG¹¹-X¹¹— and R¹²-MG¹²-X¹²— are different from each other. Inanother embodiment compounds of formula I wherein R¹¹-MG¹¹-X¹¹— andR¹²-MG¹²-X¹²— in formula I are identical to each other.

Preferred compounds of formula I are selected from the group ofcompounds of the following formulae

No. Compoud 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

wherein the alkylene spacers (—CH₂)_(n)— shown are exemplary only and ntherein is an integer of 3 or from 5 to 15, preferably an odd integer,more preferably 5, 7 or 9 and, most preferably as explicitly shown inthe respective formulae.

R¹¹ and R¹² are independently from each other as defined above,including the preferred meanings of these groups, preferably R¹¹ is F orCN, preferably R¹² is OCF₃, CF₃, F or CN, more preferably F or CN andmost preferably CN and wherein L is in each occurrence independently ofeach other F, Cl or preferably F or Cl, most preferably F.

Particularly preferred compounds are selected from the group of formulaegiven above, which bear 0, 2 or 4 F atoms in lateral positions (i.e. asL).

In a preferred embodiment of the present invention R¹¹ is OCF₃ and R¹²is OCF₃, F or CN, preferably OCF₃ or CN and most preferably CN.

The compounds of formula I can be synthesized according to or in analogyto methods which are known per se and which are described in standardworks of organic chemistry such as, for example, Houben-Weyl, Methodender organischen Chemie, Thieme-Verlag, Stuttgart. A preferred method ofpreparation can be taken from the following synthesis schemes.

The compounds of formula I are preferably accessible according to thefollowing general reaction scheme(s).

wherein n is an integer from 3 to 15 andthe conditions for the respective steps are as follows:

-   a) Pd(PPh₃)₂Cl₂, K₃PO₄, H₂O, Dioxane,-   b) H₂, Pd/C, THF,-   c) K₂CO₃, Acetone, reflux, and-   d) K₂CO₃, MEK, 80° C.

All phenylene and fused ring moieties shown in this scheme and in thefollowing schemes may independently of each other be optionally bearingone, two or three, preferably by no or one, F— or Cl—, preferably F—,atom. Fused ring moieties shown in this scheme and in the followingschemes may selected from alicyclic, aromatic and condensed groups madeup of 7 to 23 carbon atoms, wherein one or two non-adjacent CH groupseach may be replaced by an N-atom and/or one or two non-adjacent CH₂groups, independently of each other, may be replaced by an O- or anS-atom.

wherein n is as defined under Scheme I and the conditions for therespective steps are as follows:

-   a) DCC, DMAP, DCM and-   b) DCC, DMAP, DCM.

All phenylene and fused ring moieties shown in this scheme and in thefollowing schemes may independently of each other be optionally bearingone, two or three, preferably by no or one, F— or Cl—, preferably F—,atom. Fused ring moieties shown in this scheme and in the followingschemes may selected from alicyclic, aromatic and condensed groups madeup of 7 to 23 carbon atoms, wherein one or two non-adjacent CH groupseach may be replaced by an N-atom and/or one or two non-adjacent CH₂groups, independently of each other, may be replaced by an O- or anS-atom.

wherein n is as defined under Scheme I and the conditions for therespective steps are as follows:

-   a) Pd(PPh₃)₄, NaCO₃, H₂O, Toluene,-   b) BBr₃, DCM,-   c) DCC, DMAP, DCM and-   d) DCC, DMAP, DCM.

wherein n is as defined under Scheme I and the conditions for therespective steps are as follows:

-   a) Pd(PPh₃)₂Cl₂, Cu(I)I, DIPA, THF,-   b) H₂, Pd/C, THF,-   c) Pd(dppf)Cl₂, K₃PO₄, H₂O, Dioxane,-   d) NaOH, H₂O, Ethanol and-   e) DCC, DMAP, DCM.

wherein n is as defined under Scheme I and the conditions for therespective steps are as follows:

-   a) DCC, DMAP, DCM,-   b) HCl, THF and,-   c) DCC, DMAP, DCM.

wherein n is as defined under Scheme I and the conditions for therespective steps are as follows:

-   a) n-BuLi, Ether, −78° C.,-   b) Pd(PPh₃)₂Cl₂, Cu(I)I, DIPA, THF and-   c) H₂, Pd/C, THF.

wherein the alkylene spacers (—CH₂)_(n)— shown are exemplary only and ntherein is an integer of 3 or from 5 to 15, preferably 5, 7 or 9, moreas shown,

R independently in each occurrence has one of the meanings given for R¹¹and in the second occurrence alternatively may have one of theadditional meanings given for R¹² including the preferred meanings ofthese groups,

L is F or Cl, preferably F and

the conditions of the successive reactions are as exemplified underSynthesis Example 1.

All phenylene moieties shown in this scheme (and in any of the followingschemes) may independently of each other be optionally bearing one, twoor three, preferably one or two, F atoms or one Cl atom or one Cl andone F atom.

Another object of the invention is the use of bimesogenic compounds offormula I in liquid crystalline media.

Compounds of formula I, when added to a nematic liquid crystallinemixture, producing a phase below the nematic. In this context, a firstindication of the influence of bimesogenic compounds on nematic liquidcrystal mixtures was reported by Barnes, P. J., Douglas, A. G., Heeks,S. K., Luckhurst, G. R., Liquid Crystals, 1993, Vol. 13, No. 4, 603-613.This reference exemplifies highly polar alkyl spacered dimers andperceives a phase below the nematic, concluding it is a type of smectic.

A photo evidence of an existing mesophase below the nematic phase waspublished by Henderson, P. A., Niemeyer, O., Imrie, C. T. in LiquidCrystals, 2001, Vol. 28, No. 3, 463-472, which was not furtherinvestigated.

In Liquid Crystals, 2005, Vol. 32, No. 11-12, 1499-1513 Henderson, P.A., Seddon, J. M. and Imrie, C. T. reported, that the new phase belowthe nematic belonged in some special examples to a smectic C phase. Aadditional nematic phase below the first nematic was reported by Panov,V. P., Ngaraj, M., Vij, J. K., Panarin, Y. P., Kohlmeier, A., Tamba, M.G., Lewis, R. A. and Mehl, G. H. in Phys. Rev. Lett. 2010, 105,1678011-1678014.

In this context, liquid crystal mixtures comprising the new andinventive bimesogenic compounds of formula I show also a novel mesophasethat is being assigned as a second nematic phase. This mesophase existsat a lower temperature than the original nematic liquid crystallinephase and has been observed in the unique mixture concepts presented bythis application.

Accordingly, the bimesogenic compounds of formula I according to thepresent invention allow the second nematic phase to be induced innematic mixtures that do not have this phase normally. Furthermore,varying the amounts of compounds of formula I allow the phase behaviourof the second nematic to be tailored to the required temperature.

The invention thus relates to a liquid-crystalline medium whichcomprises at least one compound of the formula I.

Some preferred embodiments of the mixtures according to the inventionare indicated below.

Preferred are compounds of formula I wherein the mesogenic groups MG¹¹and MG¹² at each occurrence independently from each other comprise one,two or three six-membered rings, preferably two or three six-memberedrings.

Particularly preferred are the partial formulae II-1, II-4, II-6, II-7,II-13, II-14, II-15, II-16, II-17 and I-18.

Preferably R¹¹ and R¹² in formula I are selected of H, F, Cl, CN, NO₂,OCH₃, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, C₂F₅, OCF₃, OCHF₂, and OC₂F₅,in particular of H, F, Cl, CN, OCH₃ and OCF₃, especially of H, F, CN andOCF₃.

Typical spacer groups (Sp¹) are for example —(CH₂)_(o)—,—(CH₂CH₂O)_(p)—CH₂CH₂—, with o being 1, 3 or an integer from 5 to 40, inparticular from 1, 3 or 5 to 25, very preferably from 5 to 15, and pbeing an integer from 1 to 8, in particular 1, 2, 3 or 4.

Preferred are compounds of formula I wherein R¹¹-MG¹¹-X¹¹— andR¹²-MG¹²-X¹²— in formula I are identical.

The media according to the invention preferably comprise one, two,three, four or more, preferably one, two or three, compounds of theformula I.

The amount of compounds of formula I in the liquid crystalline medium ispreferably from 1 to 50%, in particular from 5 to 40%, very preferably10 to 30% by weight of the total mixture.

In a preferred embodiment the liquid crystalline medium according to thepresent invention comprises additionally one or more compounds offormula III, like those or similar to those known from GB 2 356 629.R³¹-MG³¹-X³¹-Sp³-X³²-MG³²-R³²  IIIwherein

-   R³¹ and R³² are each independently H, F, Cl, CN, NCS or a    straight-chain or branched alkyl group with 1 to 25 C atoms which    may be unsubstituted, mono- or polysubstituted by halogen or CN, it    being also possible for one or more non-adjacent CH₂ groups to be    replaced, in each case independently from one another, by —O—, —S—,    —NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —O—CO—O—, —S—CO—, —CO—S—,    —CH═CH—, —CH═CF—, —CF═CF— or —C≡C— in such a manner that oxygen    atoms are not linked directly to one another,-   MG³¹ and MG³² are each independently a mesogenic group,-   Sp³ is a spacer group comprising 5 to 40 C atoms, wherein one or    more non-adjacent CH₂ groups may also be replaced by —O—, —S—, —NH—,    —N(CH₃)—, —CO—, —O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O—,    —CH(halogen)-, —CH(CN)—, —CH═CH— or —C≡C—, and-   X³¹ and X³² are each independently —O—, —S—, —CO—, —COO—, —OCO—,    —O—CO—O—, —CO—NH—, —NH—CO—, —CH₂CH₂—, —OCH₂—, —CH₂O—, —SCH₂—,    —CH₂S—, —CH═CH—, —CH═CH—COO—, —OCO—CH═CH—, —C≡C— or a single bond,    and    with the condition that compounds of formula I are excluded.

The mesogenic groups MG³¹ and MG³² are preferably selected of formulaII.

Especially preferred are compounds of formula III wherein R³¹-MG³¹-X³¹—and R³²-MG³²-X³²— are identical.

Another preferred embodiment of the present invention relates tocompounds of formula III wherein R³¹-MG³¹-X³¹— and R³²-MG³²-X³²— aredifferent.

Especially preferred are compounds of formula III wherein the mesogenicgroups MG³¹ and MG³² comprise one, two or three six-membered rings verypreferably are the mesogenic groups selected from formula II as listedbelow.

For MG³¹ and MG³² in formula III are particularly preferred are thesubformulae II-1, II-4, II-6, II-7, II-13, II-14, II-15, II-16, II-17and II-18. In these preferred groups Z in each case independently hasone of the meanings of Z¹ as given in formula II. Preferably Z is —COO—,—OCO—, —CH₂CH₂—, —C≡C— or a single bond.

Very preferably the mesogenic groups MG³¹ and MG³² are selected from theformulae IIa to IIo and their mirror images.

In case of compounds with a unon-polar group, R³¹ and R³² are preferablyalkyl with up to 15 C atoms or alkoxy with 2 to 15 C atoms.

If R³¹ or R³² is an alkyl or alkoxy radical, i.e. where the terminal CH₂group is replaced by —O—, this may be straight-chain or branched. It ispreferably straight-chain, has 2, 3, 4, 5, 6, 7 or 8 carbon atoms andaccordingly is preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl,octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, or octoxy,furthermore methyl, nonyl, decyl, undecyl, dodecyl, tridecyl,tetradecyl, pentadecyl, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy ortetradecoxy, for example.

Oxaalkyl, i.e. where one CH₂ group is replaced by —O—, is preferablystraight-chain 2-oxapropyl (=methoxymethyl), 2-(=ethoxymethyl) or3-oxabutyl (=2-methoxyethyl), 2-, 3-, or 4-oxapentyl, 2-, 3-, 4-, or5-oxahexyl, 2-, 3-, 4-, 5-, or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-,7-, 8- or 9-oxadecyl, for example.

In case of a compounds with a terminal polar group, R³¹ and R³² areselected from CN, NO₂, halogen, OCH₃, OCN, SCN, COR^(x), COOR^(x) or amono- oligo- or polyfluorinated alkyl or alkoxy group with 1 to 4 Catoms. R^(x) is optionally fluorinated alkyl with 1 to 4, preferably 1to 3 C atoms. Halogen is preferably F or Cl.

Especially preferably R³¹ and R³² in formula III are selected of F, Cl,CN, NO₂, OCH₃, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, C₂F₅, OCF₃, OCHF₂,and OC₂F₅, in particular of F, Cl, CN, OCH₃ and OCF₃.

As for the spacer group Sp³ in formula III all groups can be used thatare known for this purpose to the skilled in the art. The spacer groupSp is preferably a linear or branched alkylene group having 5 to 40 Catoms, in particular 5 to 25 C atoms, very preferably 5 to 15 C atoms,in which, in addition, one or more non-adjacent CH₂ groups may bereplaced by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —O—CO—, —S—CO—, —O—COO—,—CO—S—, —CO—O—, —CH(halogen)-, —CH(CN)—, —CH═CH— or —C≡C—.

Typical spacer groups are for example —(CH₂)_(o)—,—(CH₂CH₂O)_(p)—CH₂CH₂—, —CH₂CH₂—S—CH₂CH₂— or —CH₂CH₂—NH—CH₂CH₂—, with obeing an integer from 5 to 40, in particular from 5 to 25, verypreferably from 5 to 15, and p being an integer from 1 to 8, inparticular 1, 2, 3 or 4.

Preferred spacer groups are pentylene, hexylene, heptylene, octylene,nonylene, decylene, undecylene, dodecylene, octadecylene,diethyleneoxyethylene, dimethyleneoxybutylene, pentenylene, heptenylene,nonenylene and undecenylene, for example.

Especially preferred are inventive compounds of formula III wherein Sp³is denoting alkylene with 5 to 15 C atoms. Straight-chain alkylenegroups are especially preferred.

In another preferred embodiment of the invention the chiral compounds offormula III comprise at least one spacer group Sp¹ that is a chiralgroup of the formula IV.

X³¹ and X³² in formula III denote preferably —O—, —CO—, —COO—, —OCO—,—O—CO—O— or a single bond. Particularly preferred are the followingcompounds selected from formulae III-1 to III-4:

wherein R³¹, R³² have the meaning given under formula III, Z³¹ andZ^(31-l) are defined as Z³¹ and Z³² and Z^(32-l) are respectively thereverse groups of Z³¹ and Z^(32-l) in formula III and o and r areindependently at each occurrence as defined above, including thepreferred meanings of these groups and wherein L is in each occurrenceindependently of each other preferably F, Cl, CN, OH, NO₂ or anoptionally fluorinated alkyl, alkoxy or alkanoyl group with 1 to 7 Catoms, very preferably F, Cl, CN, OH, NO₂, CH₃, C₂H₅, OCH₃, OC₂H₅,COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, OCF₃, OCHF₂, OC₂F₅, in particularF, Cl, CN, CH₃, C₂H₅, OCH₃, COCH₃ and OCF₃, most preferably F, Cl, CH₃,OCH₃ and COCH₃ and from which compounds of formula I are excluded.

Particularly preferred mixtures according to the invention comprise oneor more compounds of the formulae III-1a to III-1e and III-3a to III-3b.

wherein the parameters are as defined above.

In a preferred embodiment of the invention the liquid crystalline mediumis consisting of 2 to 25, preferably 3 to 15 compounds of formula III.

The amount of compounds of formula III in the liquid crystalline mediumis preferably from 10 to 95%, in particular from 15 to 90%, verypreferably 20 to 85% by weight of the total mixture.

Preferably, the proportion of compounds of the formulae III-1a and/orIII-1b and/or III-1c and/or III-1e and or III-3a and/or III-3b in themedium as a whole is preferably at least 70% by weight.

Particularly preferred media according to the invention comprise atleast one or more chiral dopants which themselves do not necessarilyhave to show a liquid crystalline phase and give good uniform alignmentthemselves.

Especially preferred are chiral dopants selected from formula IV

and formula V

including the respective (S,S) enantiomer,

wherein E and F are each independently 1,4-phenylene ortrans-1,4-cyclo-hexylene, v is 0 or 1, Z⁰ is —COO—, —OCO—, —CH₂CH₂— or asingle bond, and R is alkyl, alkoxy or alkanoyl with 1 to 12 C atoms.

The compounds of formula IV and their synthesis are described in WO98/00428. Especially preferred is the compound CD-1, as shown in table Dbelow. The compounds of formula V and their synthesis are described inGB 2,328,207.

Especially preferred are chiral dopants with a high helical twistingpower (HTP), in particular those disclosed in WO 98/00428.

Further typically used chiral dopants are e.g. the commerciallyavailable R/S-5011, CD-1, R/S-811 and CB-15 (from Merck KGaA, Darmstadt,Germany).

The above mentioned chiral compounds R/S-5011 and CD-1 and the compoundsof formula IV and V exhibit a very high helical twisting power (HTP),and are therefore particularly useful for the purpose of the presentinvention.

The liquid crystalline medium preferably comprises preferably 1 to 5, inparticular 1 to 3, very preferably 1 or 2 chiral dopants, preferablyselected from the above formula IV, in particular CD-1, and/or formula Vand/or R-5011 or S-5011, very preferably the chiral compound is R-5011,S-5011 or CD-1.

The amount of chiral compounds in the liquid crystalline medium ispreferably from 1 to 20%, in particular from 1 to 15%, very preferably 1to 10% by weight of the total mixture.

Further preferred are liquid crystalline media comprising one or moreadditives selected from the following formula VI

wherein

-   R⁵ is alkyl, alkoxy, alkenyl or alkenyloxy with up to 12 C atoms,

is

L¹ through L⁴ are each independently H or F,

-   Z² is —COO—, —CH₂CH₂— or a single bond,-   m is 1 or 2

Particularly preferred compounds of formula VI are selected from thefollowing formulae

wherein, R has one of the meanings of R⁵ above and L¹, L² and L³ havethe above meanings.

The liquid crystalline medium preferably comprises preferably 1 to 5, inparticular 1 to 3, very preferably 1 or 2, preferably selected from theabove formulae VIa to VIf, very preferably from formulae VIf.

The amount of suitable additives of formula VI in the liquid crystallinemedium is preferably from 1 to 20%, in particular from 1 to 15%, verypreferably 1 to 10% by weight of the total mixture.

The liquid crystal media according to the present invention may containfurther additives in usual concentrations. The total concentration ofthese further constituents is in the range of 0.1% to 10%, preferably0.1% to 6%, based on the total mixture. The concentrations of theindividual compounds used each are preferably in the range of 0.1% to3%. The concentration of these and of similar additives is not takeninto consideration for the values and ranges of the concentrations ofthe liquid crystal components and compounds of the liquid crystal mediain this application. This also holds for the concentration of thedichroic dyes used in the mixtures, which are not counted when theconcentrations of the compounds respectively the components of the hostmedium are specified. The concentration of the respective additives isalways given relative to the final doped mixture.

The liquid crystal media according to the present invention consists ofseveral compounds, preferably of 3 to 30, more preferably of 4 to 20 andmost preferably of 4 to 16 compounds. These compounds are mixed inconventional way. As a rule, the required amount of the compound used inthe smaller amount is dissolved in the compound used in the greateramount. In case the temperature is above the clearing point of thecompound used in the higher concentration, it is particularly easy toobserve completion of the process of dissolution. It is, however, alsopossible to prepare the media by other conventional ways, e.g. using socalled pre-mixtures, which can be e.g. homologous or eutectic mixturesof compounds or using so called multi-bottle-systems, the constituentsof which are ready to use mixtures themselves.

Particularly preferred mixture concepts are indicated below: (theacronyms used are explained in Table A).

The mixtures according to the invention preferably comprise

-   -   one or more compounds of formula I in a total concentration in        the range from 1 to 50%, in particular from 5 to 40%, very        preferably 10 to 30% by weight of the total mixture        and/or    -   one or more compounds of formula III in a total concentration in        the range from 10 to 95%, in particular from 15 to 90%, very        preferably 20 to 85% by weight of the total mixture, preferably        these compounds are selected from formulae III-1a to III-1e and        III-3a to III-3b especially preferred they comprise        -   N—PGI—ZI-n-Z-GP—N, preferably N—PGI—ZI-7-Z-GP—N and/or            N—PGI—ZI-9-Z-GP—N preferably in concentrations >5%, in            particular 10-30%, based on the mixture as a whole,            and/or    -   F—UIGI—ZI-n-Z-GU—F, preferably F—UIGI—ZI-9-Z-GU—F, preferably in        concentrations >5%, in particular 10-30%, based on the mixture        as a whole,        and/or    -   F—PGI—O-n-O—PP—N, preferably F—PGI—O-9-O—PP—, preferably in        concentrations of >1%, in particular 1-20%, based on the mixture        as a whole,        and/or    -   N—PP—O-n-O—PG-OT, preferably N—PP—O-7-O—PG-OT, preferably in        concentrations of >5%, in particular 5-30%, based on the mixture        as a whole,        and/or    -   N—PP—O-n-O-GU—F, preferably N—PP—O-9-O-GU—F, preferably in        concentrations of >1%, in particular 1-20%, based on the mixture        as a whole,        and/or    -   F—PGI—O-n-O-GP—F, preferably F—PGI—O-7-O-GP—F and/or        F—PGI—O-9-O-GP—F preferably in concentrations of >1%, in        particular 1-20%, based on the mixture as a whole,        and/or    -   N-GIGIGI-n-GGG-N, in particular N-GIGIGI-9-GGG-N, preferably in        concentration >5%, in particular 10-30%, based on the mixture as        a whole,        and/or    -   N—PGI-n-GP—N, preferably N—PGI-9-GP—N, preferably in        concentrations >5%, in particular 15-50%, based on the mixture        as a whole,        and/or    -   one or more suitable additives of formula VI in a total        concentration in the range from 1 to 20%, in particular from 1        to 15%, very preferably 1 to 10% by weight of the total mixture,        preferably are these compounds selected from formula VIa to VIf,        especially preferred they comprise        -   PP-n-N, preferably in concentrations of >1%, in particular            1-20%, based on the mixture as a whole,            and/or    -   one or more chiral compounds preferably in a total concentration        in the range from 1 to 20%, in particular from 1 to 15%, very        preferably 1 to 10% by weight of the total mixture, preferably        these compounds are selected from formula IV, V, and R-5011 or        S-5011, especially preferred they comprise        -   R-5011, S-5011 or CD-1, preferably in a concentration            of >1%, in particular 1-20%, based on the mixture as a            whole.

The bimesogenic compounds of formula I and the liquid crystalline mediacomprising them can be used in liquid crystal displays, such as STN, TN,AMD-TN, temperature compensation, guest-host, phase change or surfacestabilized or polymer stabilized cholesteric texture (SSCT, PSCT)displays, in particular in flexoelectric devices, in active and passiveoptical elements like polarizers, compensators, reflectors, alignmentlayers, color filters or holographic elements, in adhesives, syntheticresins with anisotropic mechanical properties, cosmetics, diagnostics,liquid crystal pigments, for decorative and security applications, innonlinear optics, optical information storage or as chiral dopants.

The compounds of formula I and the mixtures obtainable thereof areparticularly useful for flexoelectric liquid crystal display. Thus,another object of the present invention is a flexoelectric displaycomprising one or more compounds of formula I or comprising a liquidcrystal medium comprising one or more compounds of formula I.

The inventive bimesogenic compounds of formula I and the mixturesthereof can be aligned in their cholesteric phase into different statesof orientation by methods that are known to the expert, such as surfacetreatment or electric fields. For example, they can be aligned into theplanar (Grandjean) state, into the focal conic state or into thehomeotropic state. Inventive compounds of formula I comprising polargroups with a strong dipole moment can further be subjected toflexoelectric switching, and can thus be used in electrooptical switchesor liquid crystal displays.

The switching between different states of orientation according to apreferred embodiment of the present invention is exemplarily describedbelow in detail for a sample of an inventive compound of formula I.

According to this preferred embodiment, the sample is placed into a cellcomprising two plane-parallel glass plates coated with electrode layers,e.g. ITO layers, and aligned in its cholesteric phase into a planarstate wherein the axis of the cholesteric helix is oriented normal tothe cell walls. This state is also known as Grandjean state, and thetexture of the sample, which is observable e.g. in a polarizationmicroscope, as Grandjean texture. Planar alignment can be achieved e.g.by surface treatment of the cell walls, for example by rubbing and/orcoating with an alignment layer such as polyimide.

A Grandjean state with a high quality of alignment and only few defectscan further be achieved by heating the sample to the isotropic phase,subsequently cooling to the chiral nematic phase at a temperature closeto the chiral nematic-isotropic phase transition, and rubbing the cell.

In the planar state, the sample shows selective reflection of incidentlight, with the central wavelength of reflection depending on thehelical pitch and the mean refractive index of the material.

When an electric field is applied to the electrodes, for example with afrequency from 10 Hz to 1 kHz, and an amplitude of up to 12 V_(rms)/μm,the sample is being switched into a homeotropic state where the helix isunwound and the molecules are oriented parallel to the field, i.e.normal to the plane of the electrodes. In the homeotropic state, thesample is transmissive when viewed in normal daylight, and appears blackwhen being put between crossed polarizers.

Upon reduction or removal of the electric field in the homeotropicstate, the sample adopts a focal conic texture, where the moleculesexhibit a helically twisted structure with the helical axis beingoriented perpendicular to the field, i.e. parallel to the plane of theelectrodes. A focal conic state can also be achieved by applying only aweak electric field to a sample in its planar state. In the focal conicstate the sample is scattering when viewed in normal daylight andappears bright between crossed polarizers.

A sample of an inventive compound in the different states of orientationexhibits different transmission of light. Therefore, the respectivestate of orientation, as well as its quality of alignment, can becontrolled by measuring the light transmission of the sample dependingon the strength of the applied electric field. Thereby it is alsopossible to determine the electric field strength required to achievespecific states of orientation and transitions between these differentstates.

In a sample of an inventive compound of formula I, the above describedfocal conic state consists of many disordered birefringent smalldomains. By applying an electric field greater than the field fornucleation of the focal conic texture, preferably with additionalshearing of the cell, a uniformly aligned texture is achieved where thehelical axis is parallel to the plane of the electrodes in large,well-aligned areas. In accordance with the literature on state of theart chiral nematic materials, such as P. Rudquist et al., Liq. Cryst. 23(4), 503 (1997), this texture is also called uniformly-lying helix (ULH)texture. This texture is required to characterize the flexoelectricproperties of the inventive compound.

The sequence of textures typically observed in a sample of an inventivecompound of formula I on a rubbed polyimide substrate upon increasing ordecreasing electric field is given below:

Starting from the ULH texture, the inventive flexoelectric compounds andmixtures can be subjected to flexoelectric switching by application ofan electric field. This causes rotation of the optic axis of thematerial in the plane of the cell substrates, which leads to a change intransmission when placing the material between crossed polarizers. Theflexoelectric switching of inventive materials is further described indetail in the introduction above and in the examples.

It is also possible to obtain the ULH texture, starting from the focalconic texture, by applying an electric field with a high frequency, offor example 10 kHz, to the sample whilst cooling slowly from theisotropic phase into the cholesteric phase and shearing the cell. Thefield frequency may differ for different compounds.

The bimesogenic compounds of formula I are particularly useful inflexoelectric liquid crystal displays as they can easily be aligned intomacroscopically uniform orientation, and lead to high values of theelastic constant k₁₁ and a high flexoelectric coefficient e in theliquid crystal medium.

The liquid crystal medium preferably exhibits a

-   k₁₁<1×10⁻¹⁰ N, preferably <2×10⁻¹¹ N, and a flexoelectric    coefficient-   e>1×10⁻¹¹ C/m, preferably >1×10⁻¹⁰ C/m.

Apart from the use in flexoelectric devices, the inventive bimesogeniccompounds as well as mixtures thereof are also suitable for other typesof displays and other optical and electrooptical applications, such asoptical compensation or polarizing films, color filters, reflectivecholesterics, optical rotatory power and optical information storage.

A further aspect of the present invention relates to a display cellwherein the cell walls exhibit hybrid alignment conditions. The term“hybrid alignment” or orientation of a liquid crystal or mesogenicmaterial in a display cell or between two substrates means that themesogenic groups adjacent to the first cell wall or on the firstsubstrate exhibit homeotropic orientation and the mesogenic groupsadjacent to the second cell wall or on the second substrate exhibitplanar orientation.

The term “homeotropic alignment” or orientation of a liquid crystal ormesogenic material in a display cell or on a substrate means that themesogenic groups in the liquid crystal or mesogenic material areoriented substantially perpendicular to the plane of the cell orsubstrate, respectively.

The term “planar alignment” or orientation of a liquid crystal ormesogenic material in a display cell or on a substrate means that themesogenic groups in the liquid crystal or mesogenic material areoriented substantially parallel to the plane of the cell or substrate,respectively.

A flexoelectric display according to a preferred embodiment of thepresent invention comprises two plane parallel substrates, preferablyglass plates covered with a transparent conductive layer such as indiumtin oxide (ITO) on their inner surfaces, and a flexoelectric liquidcrystalline medium provided between the substrates, characterized inthat one of the inner substrate surfaces exhibits homeotropic alignmentconditions and the opposite inner substrate surface exhibits planaralignment conditions for the liquid crystalline medium.

Planar alignment can be achieved e.g. by means of an alignment layer,for example a layer of rubbed polyimide or sputtered SiO_(x), that isapplied on top of the substrate.

Alternatively it is possible to directly rub the substrate, i.e. withoutapplying an additional alignment layer. For example, rubbing can beachieved by means of a rubbing cloth, such as a velvet cloth, or with aflat bar coated with a rubbing cloth. In a preferred embodiment of thepresent invention rubbing is achieved by means of a at least one rubbingroller, like e.g. a fast spinning roller that is brushing across thesubstrate, or by putting the substrate between at least two rollers,wherein in each case at least one of the rollers is optionally coveredwith a rubbing cloth. In another preferred embodiment of the presentinvention rubbing is achieved by wrapping the substrate at leastpartially at a defined angle around a roller that is preferably coatedwith a rubbing cloth.

Homeotropic alignment can be achieved e.g. by means of an alignmentlayer coated on top of the substrate. Suitable aligning agents used onglass substrates are for example alkyltrichlorosilane or lecithine,whereas for plastic substrate thin layers of lecithine, silica or hightilt polyimide orientation films as aligning agents may be used. In apreferred embodiment of the invention silica coated plastic film is usedas a substrate.

Further suitable methods to achieve planar or homeotropic alignment aredescribed for example in J. Cognard, Mol. Cryst. Liq. Cryst. 78,Supplement 1, 1-77 (1981).

By using a display cell with hybrid alignment conditions, a very highswitching angle of flexoelectric switching, fast response times and agood contrast can be achieved.

The flexoelectric display according to present invention may alsocomprise plastic substrates instead of glass substrates. Plastic filmsubstrates are particularly suitable for rubbing treatment by rubbingrollers as described above.

Another object of the present invention is that compounds of formula I,when added to a nematic liquid crystalline mixture, produce a phasebelow the nematic.

Accordingly, the bimesogenic compounds of formula I according to thepresent invention allow the second nematic phase to be induced innematic mixtures that do not show evidence of this phase normally.Furthermore, varying the amounts of compounds of formula I allow thephase behaviour of the second nematic to be tailored to the requiredtemperature.

Examples for this are given and the mixtures obtainable thereof areparticularly useful for flexoelectric liquid crystal display. Thus,another object of the present invention is liquid crystal mediacomprising one or more compounds of formula I exhibiting a secondnematic phase.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The following examples are, therefore, to beconstrued as merely illustrative and not limitative of the remainder ofthe disclosure in any way whatsoever.

Unless the context clearly indicates otherwise, as used herein pluralforms of the terms herein are to be construed as including the singularform and vice versa.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, mean “including but not limited to”, andare not intended to (and do not) exclude other components.

Throughout the present application it is to be understood that theangles of the bonds at a C atom being bound to three adjacent atoms,e.g. in a C═C or C═O double bond or e.g. in a benzene ring, are 120° andthat the angles of the bonds at a C atom being bound to two adjacentatoms, e.g. in a C≡C or in a C≡N triple bond or in an allylic positionC═C═C are 180°, unless these angles are otherwise restricted, e.g. likebeing part of small rings, like 3-, 5- or 5-atomic rings,notwithstanding that in some instances in some structural formulae theseangles are not represented exactly.

It will be appreciated that variations to the foregoing embodiments ofthe invention can be made while still falling within the scope of theinvention. Each feature disclosed in this specification, unless statedotherwise, may be replaced by alternative features serving the same,equivalent or similar purpose. Thus, unless stated otherwise, eachfeature disclosed is one example only of a generic series of equivalentor similar features.

All of the features disclosed in this specification may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. In particular, thepreferred features of the invention are applicable to all aspects of theinvention and may be used in any combination. Likewise, featuresdescribed in non-essential combinations may be used separately (not incombination).

The total concentration of all compounds in the media according to thisapplication is 100%.

In the foregoing and in the following examples, unless otherwiseindicated, all temperatures are set forth uncorrected in degrees Celsiusand all parts and percentages are by weight.

The following abbreviations are used to illustrate the liquidcrystalline phase behavior of the compounds: K=crystalline; N=nematic;N2=second nematic; S or Sm=smectic; Ch=cholesteric; I=isotropic;Tg=glass transition. The numbers between the symbols indicate the phasetransition temperatures in ° C.

In the present application and especially in the following examples, thestructures of the liquid crystal compounds are represented byabbreviations, which are also called “acronyms”. The transformation ofthe abbreviations into the corresponding structures is straight forwardaccording to the following three tables A to C.

All groups C_(n)H_(2n+1), C_(m)H_(2m+1), and C_(l)H2_(l+1) arepreferably straight chain alkyl groups with n, m and l C-atoms,respectively, all groups C_(n)H_(2n), C_(m)H_(2m) and C_(l)H_(2l) arepreferably (CH₂)_(n), (CH₂)_(m) and (CH₂)_(l), respectively and —CH═CH—preferably is trans-respectively E vinylene.

Table A lists the symbols used for the ring elements, table B those forthe linking groups and table C those for the symbols for the left handand the right hand end groups of the molecules.

Table D lists exemplary molecular structures together with theirrespective codes.

TABLE A Ring Elements C

P

D

DI

A

AI

G

GI

G(Cl)

GI(Cl)

G(1)

GI(1)

U

UI

Y

M

MI

N

NI

nn

nnI

np

n3f

n3fI

th

thI

th2f

th2fI

o2f

o2fI

dh

K

KI

L

LI

F

FI

TABLE B Linking Groups n (—CH₂—)_(n) “n” is an integer except 0 and 2 E—CH₂—CH₂— V —CH═CH— T —C≡C— W —CF₂—CF₂— B —CF═CF— Z —CO—O— ZI —O—CO— X—CF═CH— XI —CH═CF— 1O —CH₂—O— O1 —O—CH₂— Q —CF₂—O— QI —O—CF₂—

TABLE C End Groups Left hand side, used alone or Right hand side, usedalone or in combination with others in combination with others -n-C_(n)H_(2n+1)— -n —C_(n)H_(2n+1) -nO- C_(n)H_(2n+1)—O— -nO—O—C_(n)H_(2n+1) -V- CH₂═CH— -V —CH═CH₂ -nV- C_(n)H_(2n+1)—CH═CH— -nV—C_(n)H_(2n)—CH═CH₂ -Vn- CH₂═CH—C_(n)H_(2n)— -Vn —CH═CH—C_(n)H_(2n+1)-nVm- C_(n)H_(2n+1)—CH═CH—C_(m)H_(2m)— -nVm—C_(n)H_(2n)—CH═CH—C_(m)H_(2m+1) -N- N≡C— -N —C≡N -S- S═C═N— -S —N═C═S-F- F— -F —F -CL- Cl— -CL —Cl -M- CFH₂— -M —CFH₂ -D- CF₂H— -D —CF₂H -T-CF₃— -T —CF₃ -MO- CFH₂O— -OM —OCFH₂ -DO- CF₂HO— -OD —OCF₂H -TO- CF₃O—-OT —OCF₃ -A- H—C≡C— -A —C≡C—H -nA- C_(n)H_(2n+1)—C≡C— -An—C≡C—C_(n)H_(2n+1) -NA- N≡C—C≡C— -AN —C≡C—C≡N Left hand side, used inRight hand side, used in combination with others only combination withothers only - . . . n . . . - (—CH₂—)_(n) - . . . n . . . (—CH₂—)_(n) -. . . M . . . - —CFH— - . . . M . . . —CFH— - . . . D . . . - —CF₂— - .. . D . . . —CF₂— - . . . V . . . - —CH═CH— - . . . V . . . —CH═CH— - .. . Z . . . - —CO—O— - . . . Z . . . —CO—O— - . . . ZI . . . - —O—CO— -. . . ZI . . . —O—CO— - . . . K . . . - —CO— - . . . K . . . —CO— - . .. W . . . - —CF═CF— - . . . W . . . —CF═CF—wherein n und m each are integers and three points “. . . ” indicate aspace for other symbols of this table.

Preferably the liquid crystalline media according to the presentinvention comprise, besides the compound(s) of formula I one or morecompounds selected from the group of compounds of the formulae of thefollowing table.

TABLE D In this table n is an integer selected from 3 and 5 to 15,preferably from 3, 5, 7 and 9, unless explicitly defined otherwise.

F-PGI-O-n-O-GP-F

F-PG-O-n-O-GIP-F

N-PP-O-n-O-GU-F

N-PP-O-n-O-PG-OT

F-PGI-O-n-O-PP-N

R-5011 respectively S-5011

CD-1

PP-n-N (n ϵ {2; 3; 4; 5; 6; 7})

PPP-n-N (n ϵ {2; 3; 4; 5; 6; 7})

CC-n-V (n ϵ {2; 3; 4; 5; 7})

CEPGI-n-m (n ϵ {2; 3; 4; 5}; m ϵ {2; 3; 4; 5})

F-UIGI-ZI-n-Z-GU-F

N-PGI-ZI-n-Z-GP-N

F-PGI-ZI-n-Z-GP-N

F-PGI-ZI-n-Z-PP-N

N-GIGIGI-n-GGG-N

N-PGIUI-n-UGP-N

N-GIUIGI-n-GUG-N

N-GIUIP-n-PUG-N

N-PGI-n-GP-N

N-PUI-n-UP-N

N-UIUI-n-UU-N

N-GIGI-n-GG-N

N-PGI(1)-n-G(1)P-N

F-UIGI-n-GU-F

UIP-n-PU

N-PGI-n-GP-N

N-PG(1)-n-GI(1)P-N

N-PZIP-n-PZP-N

N-GIZIP-n-PZG-N

N-PZIGI-n-GZP-N

N-GIZIGI-n-GZG-N

N-UIZIP-n-PZU-N

N-UIZIGI-n-GZU-N

F-PZIP-n-PZP-F

F-GIZIP-n-PZG-F

F-PZIGI-n-GZP-F

F-GIZIGI-n-GZG-F

F-UIZIP-n-PZU-F

F-UIZIGI-n-GZU-F

N-PGIZIP-n-PZGP-N

N-GIGIZIP-n-PZGG-N

N-PGIZIGI-n-GZGP-N

N-GIGIZIGI-n-GZGG-N

N-PO1GI-n-GO1P-N

N-PQIGI-n-GQP-N

F-PO1P-n-PO1P-N(═N-PO1P-n-PO1P-F)

F-PO1GI-n-GO1P-N(═N-PO1GI-n-GO1P-F)

2(CHCH3)1-PPZIP-O-n-O-PP-N

TO-GIP-ZI-n-Z-PG-OT

TO-PGI-ZI-n-Z-GP-OT

TO-GIGI-ZI-n-Z-GG-OT

TO-GIP-ZI-n-Z-PP-N

TO-PGI-ZI-n-Z-PP-N

TO-GIGI-ZI-n-Z-GP-N

TO-GIP-O-n-O-PG-OT

TO-P-T-n-T-P-OT

F-PGI-O-n-O-PG-OT

TO-GIP-O-n-O-PP-N

T-PGI-ZI-n-Z-GP-T

T-PGI-n-GP-T

T-UIQIUI-n-UQU-T

F-PGI-ZI-n-O-PP-N

N-PGI-ZI-n-O-GP-N

N-PGI-ZI-n-GP-N

N-PP-ZI-n-PP-N

N-PGI-ZI-n-GP-N

F-PGI-ZI-n-GP-F

N-PP-SCO-n-COS-PP-N

N-PGI-SCO-n-COS-GP-N

F-PGI-SCO-n-COS-GP-F

F-GIP-SCO-n-COS-PG-F

F-GIP-SCO-n-COS-PP-N

F-GIP-SCO-n-COS-PGG-N

N-PP-S-9-S-PP-N

N-PGI-S-n-S-GP-N

F-PGI-ZI-n-Z-PUU-N

N-GI-ZIO-n-Z-8G-N

F-PGI-O-n-O-np-N

F-PGI-ZI-n-Z-np-N

F-GIGI-ZI-n-Z-np-N

F-GIGI--n-Z-np-N

H-nnI-ZI-n-Z-PP-N

H-nnI-ZI-n-Z-P-F

COMPOUND AND SYNTHESIS EXAMPLES Synthesis Example 1 Preparation of

The compound of interest is prepared according to the following scheme.

Stage 1.1

4-benzyloxy-2-fluorobromobenzene (219 g, 0.78 mol),4-fluorobenzene-boronic acid (109 g, 0.78 mol), dioxane (900 ml), water(450 ml) and potassium phosphate hydrate (180 g, 0.78 mol) are placed inan ultrasonic bath (a procedure is called short “ultrasonicated” in thisapplication) for 30 minutes.[1,1-Bis(diphenylphosphino)ferrocene]-dichloropalladium(II) (6.4 g, 8.8mmol) is added and the mixture heated under reflux for 4 hours. Themixture is cooled and the two layers are separated. The aqueous layer isextracted twice with toluene. The organic phases are combined andevaporated in vacuo. The residue is purified by vacuum flashchromatography on silica eluting with dichloromethane. The product isobtained as a white solid.

Stage 1.2

4-(benzyloxy)-2-fluoro-1-(4-fluorophenyl)benzene (195 g, 0.658 mol),tetrahydrofuran (1,500 ml) and palladium on carbon (10%, 20 g) arehydrogenated at 30° C. for 4 hours. The catalyst is filtered off and thesolvent is removed in vacuo to give 3-fluoro-4-(4-fluorophenyl)phenol.

Stage 1.3

4-Cyanonaphthol (10.0 g, 59.1 mmol) is dissolved in acetone (300 ml) ina round bottomed flask. Potassium carbonate (16.6 g, 120 mmol) is addedunder stirring and the mixture is heated under reflux for 1 hour. Themixture is cooled to ambient temperature (which means approximately 20°C. in the present application and is also called colloquially “roomtemperature” sometimes) and then an excess of 1,9-dibromononane (120.1g, 420 mmol) is added. The reaction mixture is heated under reflux andstirred for 16 hours. Then the solution allowed to cool and subsequentlyfiltered in vacuo and washed with acetone. The filtrate is concentratedin vacuo to yield a yellow liquid. Petroleum ether is added and thesolution cooled to 0° C. A white solid precipitates, which is collectedand purified by column chromatography through silica gel, eluting withdichloromethane in petroleum ether as eluent (7:3 ratio). Theappropriate fractions containing the product are combined and thesolvent is removed in vacuo to yield the product.

Stage 1.4

6-(9-Bromo-nonyloxy)-naphthalene-2-carbonitrile (7.70 g, 20.57 mmol) and3-fluoro-4-(4-fluorophenyl)phenol (4.24 g, 20.57 mmol) are charged intoa 250 ml 3-neck round bottomed flask containing butanone (100 ml).

Potassium carbonate (30.41 g, 220.00 mmol) is added. The reactionmixture is stirred for 16 hours at a temperature of 80° C. The mixtureis then cooled to ambient temperature and the solid is filtered off. Theorganic phase is washed with water (50 ml), dried over magnesiumsulphate and evaporated under educed pressure. The pure product isobtained by crystallisation from acetonitrile.

The physical properties of this compound make the material very usefulfor mixtures comprising bimesogenic compounds, in particular for use inthe USH and in the ULH mode.

Synthesis Example 2 Preparation of

The compound of interest is prepared according to the following scheme.

Stage 2.1

Decanedioic acid (5.00 g, 24.72 mmol), dicyclohexylcarbodiimide (5.10 g,24.72 mmol) and dimethylaminopyridine (301.86 mg, 2.47 mmol) are chargedinto a flask containing 80 ml dichloromethane at ambient temperature.The reaction mixture is stirred for 30 min, then2,4′-difluoro-biphenyl-4-ol (5.10 g, 24.72 mmol) is added. The reactionmixture is stirred at ambient temperature for 16 hours. Water (50 ml) isadded, the organic phase is separated from the aqueous phase, dried overmagnesium sulphate and the solvent is evaporated. Purification by columnchromatography on silica gel dichloromethane:ethyl acetate (4:6 ratio)yielded decanedioic acid mono-(2,4′-difluoro-biphenyl-4-yl) ester.

Stage 2.2

Decanedioic acid mono-(2,4′-difluoro-biphenyl-4-yl) ester (3.00 g, 7.68mmol), dicyclohexylcarbodiimide (1.59 g, 7.68 mmol) anddimethylaminopyridine (93.82 mg, 0.77 mmol) are charged to a flaskcontaining dichloromethane (50 ml) at ambient temperature. The mixtureis stirred for 30 min, then 6-hydroxy-naphthalene-2-carbonitrile (1.30g, 7.68 mmol) is added. The resulting mixture is stirred at ambienttemperature for 16 hours. Water (20 ml) is added, and then organic phaseis separated, dried over magnesium sulphate and evaporated. Purificationby column chromatography on silica gel dichloromethane:ethyl acetate(8:2 ratio) yields 6-cyanonaphthalen-2-yl3-fluoro-4-(4-fluorophenyl)phenyl decanedioate (3.20 g) as a whitesolid.

Synthesis Example 3 Preparation of

The compound of interest is prepared according to the following scheme.

Stage 3.1

Undecanedioic acid (10.49 g, 48.50 mmol), dicyclohexylcarbodiimide(10.01 g, 48.50 mmol) and dimethylaminopyridine (592.18 mg, 4.85 mmol)are charged to an flask and containing 100 ml dichloromethane at ambienttemperature. After stirring for 30 min 2,4′-difluoro-biphenyl-4-ol(10.00 g, 48.50 mmol, 1.00 eq.) is added. The reaction mixture isstirred at ambient temperature for 16 hours. Water (50 ml) is added, theorganic phase is separated, dried over magnesium sulphate andevaporated. Purification by column chromatography on silica geldichloromethane:ethyl acetate (4:6 ratio) yields the desired product.

Stage 3.2

11-[3-fluoro-4-(4-fluorophenyl)phenoxy]-11-oxoundecanoic acid (5.00 g,12.36 mmol), dicyclohexylcarbodiimide (2.55 g, 12.36 mmol) anddimethylaminopyridine (150.95 mg, 1.24 mmol, 0.10 eq.) are charged to aflask containing 50 ml dichloromethane at ambient temperature. Thereaction mixture is stirred for 30 min then6-hydroxy-naphthalene-2-carbonitrile (2.30 g, 13.60 mmol) is added andstirred at ambient temperature for 16 hours. Water (20 ml) is added, theorganic phase is separated, dried over magnesium sulphate andevaporated. Crude is purified by column chromatography through silicagel, eluting with dichloromethane:Petroleum ether as eluent (1:1 ratio).The appropriate fractions containing the product are combined and thesolvent is removed in vacuo to yield 6-cyanonaphthalen-2-yl3-fluoro-4-(4-fluorophenyl)phenyl undecanedioate (5.70 g).

Synthesis Example 4 Preparation of

The compound of interest is prepared according to the following scheme.

Stage 4.1

A solution of (4-methoxyphenyl)boronic acid (9.75 g, 64.17 mmol) in 20ml ethanol is added dropwise to a stirred solution of4-bromo-benzonitrile (10.00 g, 54.94 mmol),tetrakis(triphenylphosphin)-palladium(0) (1.92 g, 1.66 mmol) in 50 mltoluene and sodium carbonate (2 M, 91.57 ml, 183.13 mmol). The mixtureis heated to reflux for 3 h. After reaction is completed, it is cooledto ambient temperature. Water (20 ml) is added, the organic phase isseparated, dried over magnesium sulphate and evaporated. Purification bycolumn chromatography on silica, dichloromethane yields pure4′-Methoxy-biphenyl-4-carbonitrile.

Stage 4.2

1.0 M dichloromethane solution of boron tribromide (48.78 ml, 48.78mmol) is added dropwise to a solution of4′-methoxy-biphenyl-4-carbonitrile (10.00 g, 47.79 mmol) in 50 ml drydichloromethane at −78° C. The reaction mixture is allowed to reachambient temperature and is stirred for 16 hours. The reaction mixture iscooled to 0° C. and quenched by adding 50 ml water. The organic phase isseparated from the aqueous phase, dried over magnesium sulphate andevaporated. Purification by column chromatography on silica geldichloromethane:ethyl acetate (8:2 ratio) yields pure4′-hydroxy-biphenyl-4-carbonitrile.

Stage 4.3

Heptanedioic acid (5.00 g, 31.22 mmol), dicyclohexylcarbodiimide (6.44g, 31.22 mmol) and dimethylaminopyridine (381.16 mg, 3.12 mmol) arecharged to a flask containing dichloromethane (50 ml) at ambienttemperature. The mixture is stirred for 30 min, then4′-hydroxy-biphenyl-4-carbonitrile (6.09 g, 31.22 mmol) is added andstirred at ambient temperature for 16 hours. Water (20 ml) is added, theorganic phase is separated, dried over magnesium sulphate andevaporated. Purification by column chromatography on silica geldichloromethane:ethyl acetate (6:4) yields heptanedioic acidmono-(4′-cyano-biphenyl-4-yl) ester.

Stage 4.4

Heptanedioic acid mono-(4′-cyano-biphenyl-4-yl) ester (900.00 mg, 2.67mmol), dicyclohexylcarbodiimide (550 mg, 2.67 mmol) anddimethylaminopyridine (32.57 mg, 0.26 mmol) are charged to a flaskcontaining dichloromethane (20 ml) at ambient temperature. The mixtureis stirred for 30 min, then quinolin-6-ol (425.96 mg, 2.93 mmol) isadded. The reaction mixture is stirred at ambient temperature for 16hours. Water (20 ml) is added, the organic phase is separated, driedover magnesium sulphate and evaporated. Purification by columnchromatography on silica gel dichloromethane:ethyl acetate (7:3 ratio)yields 4-(4-cyanophenyl)phenyl quinolin-6-yl heptanedioate.

Synthesis Example 5 Preparation of

The compound of interest is prepared according to the following scheme.

Stage 5.1

Nonanedioic acid (8.0 g, 42.50 mmol), dicyclohexylcarbodiimide (8.77 g,42.5 mmol) and dimethylaminopyridine (518.96 mg, 4.25 mmol) are chargedto a flask containing 50 ml dichloromethane at ambient temperature. Themixture is stirred for 30 min, then 4-fluoro-phenol (4.76 g, 42.50 mmol)is added. The resulting mixture is stirred at ambient temperature for 16hours. Water 20 ml is added, and organic phase is separated, dried overmagnesium sulphate and evaporated. Purification by column chromatographyon silica gel dichloromethane:ethyl acetate (1:4 ratio) yields9-(4-fluorophenoxy)-9-oxononanoic acid.

Stage 5.2

Nonanedioic acid mono-(4-fluoro-phenyl) ester (2.00 g, 7.08 mmol),dicyclohexylcarbodiimide (1.46 g, 7.08 mmol) and dimethylaminopyridine(86.50 mg, 0.70 mmol) are charged to a flask containing 50 mldichloromethane at ambient temperature. The mixture is stirred for 30min, and then quinolin-6-ol (1.03 g, 7.08 mmol) is added. The reactionmixture is stirred at ambient temperature for 16 hours. Water (20 ml) isadded, the organic phase is separated, dried over magnesium sulphate andevaporated. Purification by column chromatography on silica gel, usingdichloromethane:ethyl acetate (1:1 ratio) as an eluent, yields4-fluorophenyl quinolin-6-yl nonanedioate (2.35 g).

Synthesis Example 6 Preparation of

The compound of interest is prepared according to the following scheme.

Stage 6.1

Methyl 5-hexynoate (15.5 g, 122.86 mmol), 4-bromo-3-fluoroiodobenzene(36.97 g, 122.86 mmol), diisopropylamine (45 ml) are added in a flaskcontaining tetrahydrofuran (225 ml). The flask is flushed with nitrogen,Pd(Ph₃P)₂Cl₂ (330 mg) and CuI (165 mg) are added to the mixture, whichis then warmed to 30° C. for 20 minutes and then 40° C. for 1 hour. Themixture is cooled and the solids filtered off and washed through withEthyl acetate. The organic phase is evaporated. The crude is purified bycolumn chromatography on Silica, eluted with petroleum ether:dichloromethane (2:1 ratio) and then Petroleum ether: dichloromethane(1:1 ratio). The appropriate fractions are combined and concentrated togive the product.

Stage 6.2

Platinum on carbon (2.7 g, 10% on carbon) is placed under a nitrogenatmosphere in a 1 liter 3 necked round bottom flask. To thistetrahydrofuran (270 ml) and methyl6-(4-bromo-3-fluorophenyl)hex-5-ynoate (26.9 g, 89.9 mmol) are added.The flask is twice flushed with hydrogen gas from a balloon. The mixtureis then stirred very vigorously for 5 hours under a hydrogen atmosphere.The mixture is filtered through celite to give a clear solution. This isconcentrated under reduced pressure to give the product.

Stage 6.3

Under a nitrogen atmosphere, a mixture of methyl6-(4-bromo-3-fluorophenyl)hexanoate (26 g, 86.9 mmol),3,4-difluorobenzeneboronic acid (13.74 g, 87 mmol), potassium phosphate(72.7 g, 316 mmol), dioxan (160 ml) water (80 ml) and Pd(dppf)Cl₂ (615mg) are “ultrasonicated” for 30 minutes and then heated to 90° C. for 16hours. The mixture is cooled to ambient temperature. The organic phaseis separated, dried over magnesium sulphate and concentrated underreduced pressure. The crude is purified on a column of silica elutedwith petroleum ether: dichloromethane (1:1 ratio) which yields theproduct as clear oil.

Stage 6.4

Methyl 6-[4-(3,4-difluorophenyl)-3-fluorophenyl]hexanoate (22 g, 65.4mmol), sodium hydroxide (5.23 g, 131 mmol), ethanol (100 ml) and water(100 ml) are heated to 100° C. for 2 hours. The mixture is then cooledto ambient temperature. The volume of the reaction mixture is reduced byhalf under reduced pressure, and then the reaction mixture is acidifiedwith concentrated hydrochloric acid. The crude mixture is cooled in anice bath and the resulting solid is filtered off and washed with water.Recrystallisation from ethanol:water (1:1 ratio) yields the desiredproduct.

Stage 6.5

6-[4-(3,4-difluorophenyl)-3-fluorophenyl]hexanoic acid (3.00 g, 9.31mmol), dicyclohexylcarbodiimide (1.92 g, 9.31 mmol) anddimethylaminopyridine (113.64 mg, 0.93 mmol) are charged to a flaskcontaining 50 ml dichloromethane at ambient temperature. The mixture isstirred for 30 min then 6-hydroxy-naphthalene-2-carbonitrile (1.57 g,9.31 mmol, 1.00 eq.) is added and the reaction mixture is stirred atambient temperature for 16 hours. Then water (20 ml) is added, theorganic phase is separated from the aqueous phase, dried over magnesiumsulphate and the solvent is evaporated. Purification by columnchromatography on silica gel petroleum ether:dichloromethane (1:1 ratio)yields 6-cyanonaphthalen-2-yl6-[4-(3,4-difluorophenyl)-3-fluorophenyl]hexanoate.

Synthesis Example 7 Preparation of

The compound of interest is prepared according to the following scheme.

Stage 7.1

6-[4-(3,4-difluorophenyl)-3-fluorophenyl]hexanoic acid (3.00 g, 9.31mmol), dicyclohexylcarbodiimide (1.92 g, 9.31 mmol) anddimethylaminopyridine (113.64 mg, 0.93 mmol) are charged to a flaskcontaining 50 ml dichloromethane at ambient temperature. The mixture isstirred for 30 min then quinolin-6-ol (1.35 g, 9.31 mmol) is added andstirred at ambient temperature for 16 hours. Water (20 ml) is added, theorganic phase is separated, dried over magnesium sulphate andevaporated. Purification by column chromatography on silica geldichloromethane:ethyl acetate (3:1 ratio) yields quinolin-6-yl6-[4-(3,4-difluorophenyl)-3-fluorophenyl]hexanoate.

Synthesis Example 8 Preparation of

The compound of interest is prepared according to the following scheme.

Stage 8.1

6-Acetoxy-naphthalene-2-carboxylic acid (16.00 g, 69.50 mmol) and3,4,5-trifluoro-phenol (10.29 g, 69.50 mmol) are in a flask containing300 ml dichloromethane. N,N′-Diisopropylcarbodiimide (8.77 g, 69.50mmol) and dimethylaminopyridine (0.85 g, 6.95 mmol) are added and thesolution is stirred for 16 hours. The solids are filtered off and theorganic layer is concentrated to yield a white solid. Purification bycolumn chromatography on silica gel petroleum ether:dichloromethane (7:3ratio) yields 3,4,5-trifluorophenyl6-(acetyloxy)naphthalene-2-carboxylate.

Stage 8.2

3,4,5-Trifluorophenyl 6-(acetyloxy)naphthalene-2-carboxylate (19.00 g,52.74 mmol) in tetrahydrofuran (250 ml) is treated with HCl (5M, 150.00ml, 3246.58 mmol) and stirred at ambient temperature for 16 hours.Diethyl ether (100 ml) is added and the organic phase is separated fromthe aqueous phase, washed with water, dried over magnesium sulphate, andthe solvent is evaporated. Recrystallisation from acetonitrile yields3,4,5-trifluorophenyl 6-hydroxynaphthalene-2-carboxylate.

Stage 8.3

3,4,5-Trifluorophenyl 6-hydroxynaphthalene-2-carboxylate (5.96 g, 18.73mmol), pimelic Acid (1.50 g, 9.37 mmol), are added to a flask containing100 ml dichloromethane. Dicyclohexylcarbodiimide (2.55 g, 12.36 mmol)and dimethylaminopyridine (340 mg, 2.81 mmol) are added and stirred atambient temperature for 16 hours. Water (50 ml) is added and organicphase is separated, dried over magnesium sulphate and evaporated.Purification by column chromatography on silica geldichloromethane:ethyl acetate (4:1 ratio) yieldsbis[6-(3,4,5-trifluorophenoxycarbonyl)naphthalen-2-yl]heptanedioate.

Synthesis Example 9 Preparation of

The compound of interest is prepared according to the following scheme.

Stage 9.1

n-Butyllithium solution (1.6 M in hexane, 115.00 ml, 195.51 mmol) isadded to the solution of 2-bromo-6-fluoro-naphthalene (20.00 g, 88.87mmol) in 300 ml ether at −78° C. The mixture is stirred at −78° C. for 1h and a solution of iodine (27.07 g, 106.64 mmol) in ether (100 ml) isadded via cannula. The mixture is warmed to ambient temperature over aperiod of approximately 1 h, quenched with saturated aqueous solution ofammonium chloride, washed with saturated aqueous Sodium thiosulfate,washed with water and brine, dried over magnesium sulphate andconcentrated under reduced pressure.

The residue is purified via flash chromatography using petroleum etherto give 2-fluoro-6-iodo-naphthalene.

Stage 9.2

Hepta-1,6-diyne (3.73 ml, 32.56 mmol) is added to a flask containing 30ml tetrahydrofuran followed by bis triphenylphsophine dichloro palladium(87.09 mg, 0.12 mmol), copper iodide (18.58 mg, 0.10 mmol) anddiisopropylamine (12.00 ml, 85.62 mmol). The flask is purged withnitrogen. 2-fluoro-6-iodo-naphthalene (18.60 g, 68.38 mmol). Thereaction mixture is stirred at ambient temperature for 3 h. The solidsfiltered off and washed through with dichloromethane. The organic phaseis evaporated. The crude is purified by column chromatography on Silica,eluted with Petroleum ether. The appropriate fractions are combined andconcentrated to give2-fluoro-6-[7-(6-fluoronaphthalen-2-yl)hepta-1,6-diyn-1-yl]naphthalene(11.63 g).

Stage 9.3

Platinum on carbon (775 mg, 10% on carbon) is added to a flaskcontaining 250 ml tetrahydrofuran. To this2-fluoro-6-[7-(6-fluoronaphthalen-2-yl)hepta-1,6-diyn-1-yl]naphthalene(10.0 g, 26.29 mmol) is added. The flask is twice flushed with hydrogengas from a balloon. The mixture is then stirred very vigorously for 5hours under a hydrogen atmosphere. The mixture is filtered throughcelite to give a clear solution. This is concentrated under reducedpressure to give the product.

Compound Examples 10 and Following

The following compounds of formula I are prepared analogously.

No. Compound 10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

The materials in the above table generally show increased performance inthe screening mixtures, as compared to known, more conventionalbimesogenic compounds as e.g. those shown in the table below.

Comparative Compound Example 1

Phase sequence: K 98 (N 83) I, e/K=2.25 V⁻¹.

Use Examples, Mixture Examples

Typically a 5.6 μm thick cell, having an anti-parallel rubbed PIalignment layer, is filled on a hotplate at a temperature at which theflexoelectric mixture in the isotropic phase.

After the cell has been filled phase transitions, including clearingpoint, are measured using Differential Scanning Calorimetry (DSC) andverified by optical inspection. For optical phase transitionmeasurements, a Mettler FP90 hot-stage controller connected to a FP82hot-stage is used to control the temperature of the cell. Thetemperature is increased from ambient temperature at a rate of 5 degreesC. per minute, until the onset of the isotropic phase is observed. Thetexture change is observed through crossed polarizers using an OlympusBX51 microscope and the respective temperature noted.

Wires are then attached to the ITO electrodes of the cell using indiummetal. The cell is secured in a Linkam THMS600 hot-stage connected to aLinkam TMS93 hot-stage controller. The hot-stage is secured to arotation stage in an Olympus BX51 microscope.

The cell is heated until the liquid crystal is completely isotropic. Thecell is then cooled under an applied electric field until the sample iscompletely nematic. The driving waveform is supplied by a TektronixAFG3021B arbitrary function generator, which is sent through aNewtons4th LPA400 power amplifier before being applied to the cell. Thecell response is monitored with a Thorlabs PDA55 photodiode. Both inputwaveforms and optical response are measured using a Tektronix TDS 2024Bdigital oscilloscope.

In order to measure the flexoelastic response of the material, thechange in the size of the tilt of the optic axis is measured as afunction of increasing voltage. This is achieved by using the equation:

${\tan\mspace{11mu}\varphi} = {\frac{P_{0}}{{2\;\pi}\;}\frac{e}{K}\underset{\_}{E}}$wherein φ is the tilt in the optic axis from the original position (i.e.when E=0), E is the applied field, K is the elastic constant (average ofK₁ and K₃) and e is the flexoelectric coefficient (where e=e₁+e₃). Theapplied field is monitored using a HP 34401A multimeter. The tilt angleis measured using the aforementioned microscope and oscilloscope. Theundisturbed cholesteric pitch, P₀, is measured using an Ocean OpticsUSB4000 spectrometer attached to a computer. The selective reflectionband is obtained and the pitch determined from the spectral data.

The mixtures shown in the following examples are well suitable for usein USH-displays. To that end an appropriate concentration of the chiraldopant or dopants used has to be applied in order to achieve acholesteric pitch of 200 nm or less.

Host Mixture H-0

The host mixture H-0 is prepared and investigated.

Composition Compound No. Abbreviation Conc./% 1 F-PGI-O-9-O-GP-F 25.0 2F-PGI-O-9-O-PP-N 25.0 3 F-PGI-ZI-9-Z-GP-F 25.0 4 F-PGI-ZI-9-Z-PP-N 25.0Σ 100.0

Comparative Mixture Example Mixture C-1

Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2F-PGI-O-9-O-GP-F 24.5 3 F-PGI-O-9-O-PP-N 24.5 4 F-PGI-ZI-9-Z-GP-F 24.5 5F-PGI-ZI-9-Z-PP-N 24.5 Σ 100.0

This mixture (C-1) is prepared and investigated. It is well suitable forthe USH-mode. It has a cholesteric pitch of 301 nm at 35° C. The e/K ofthis mixture is 1.90 C·m⁻¹N⁻¹, which corresponds to 1.90 V⁻¹, at atemperature of 34.8° C.

Mixture Example 1 Mixture M-1

Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2F-PGI-O-9-O-GP-F 22.0 3 F-PGI-O-9-O-PP-N 22.0 4 F-PGI-ZI-9-Z-GP-F 22.0 5F-PGI-ZI-9-Z-PP-N 22.0 6 Example Compound 1 10.0 Σ 100.0

This mixture (M-1) is prepared and investigated. It is well suitable forthe USH-mode and especially for the ULH-mode. has a cholesteric pitch of360 nm at 44° C. The e/K of this mixture is 2.03 Cm⁻¹N⁻¹ at atemperature of 44° C.

Mixture Example 2 Mixture M-2

The following mixture is prepared (Mixture M-2) and investigated.

Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2F-PGI-O-9-O-GP-F 22.0 3 F-PGI-O-9-O-PP-N 22.0 4 F-PGI-ZI-9-Z-GP-F 22.0 5F-PGI-ZI-9-Z-PP-N 22.0 6 Example Compound 2 10.0 Σ 100.0

This mixture (M-2) is prepared and investigated. It is well suitable forthe USH-mode and especially for the ULH-mode. It has a cholesteric pitchof 303 nm at 44° C. The e/K of this mixture is 1.96 C·m⁻¹N⁻¹ at atemperature of 44° C.

Mixture Example 3 Mixture M⁰-3

Composition Compound No. Abbreviation Conc./% 1 F-PGI-ZI-9-Z-PP-N 15.002 F-PGI-O-9-O-np-N 10.00 3 F-PGI-ZI-7-Z-PP-N 10.00 4 F-PGI-ZI-9-Z-PUU-N15.00 5 F-UIGI-ZI-9-Z-GP-N 10.00 6 N-GI-ZI-9-Z-G-N 10.00 7F-PGI-ZI-9-Z-np-N 15.00 8 H-nnI-ZI-5-Z-PP-N 5.00 9 H-nnI-ZI-7-Z-P-F 5.0010 F-GIGI5-Z-np-N 5.00 Σ 100.0

This mixture (M⁰-3) is prepared. A mixture is made up of 98% (by mass)of mixture M^(o)-3 and 2% of R-5011 are combined and the resultantmixture (M-3) is then investigated. This mixture (M-3) is well suitablefor the USH-mode and especially for the ULH-mode. It has a cholestericpitch of 312 nm at 35° C. The e/K of this mixture is 3.05 C·m⁻¹N⁻¹ at atemperature of 35° C.

The invention claimed is:
 1. Bimesogenic compounds of formula

wherein R¹¹ and R¹² are each independently H, halogen, CN, NO₂ or a straight-chain or branched alkyl group with 1 to 25 C atoms which may be unsubstituted, mono-or polysubstituted by halogen or CN, wherein one or more non-adjacent CH₂ groups may be replaced, in each occurrence independently from one another, by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —O—CO—O—, —S—CO—, —CO—S—, —CH═CH—, —CH═CF—, —CF═CF— or —C≡C— in such a manner that oxygen atoms are not linked directly to one another, MG¹¹ and MG¹² are each independently a mesogenic group, at least one of MG¹¹ and MG¹² contains at least one fused ring group selected from alicyclic, aromatic and condensed groups made up of 7 to 23 carbon atoms, wherein one or two non-adjacent CH groups each may be replaced by an N-atom and/or one or two non-adjacent CH₂ groups, independently of each other, may be replaced by an O- or an S-atom, and which optionally is substituted by one or more halogen atoms, and/or by one or more alkyl group(s) each independently having 1 to 9 C atoms, and/or by one more alkoxy group(s) each independently having 1 to 9 C atoms, wherein the mesogenic group can also contain 0 to 3 six membered rings selected from 1,4-phenylene, wherein in addition one or more CH groups may be replaced by N, trans-1,4-cyclo-hexylene in which, in addition, one or two non-adjacent CH₂ groups may be replaced by O and/or S, 1,4-cyclohexenylene, 1,4-bicyclo-(2,2,2)-octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydro-naphthalene-2,6-diyl, 1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl, spiro[3.3]heptane-2,6-diyl or dispiro[3.1.3.1] decane-2,8-diyl, it being possible for all these groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkenyl, alkoxy, alkenyloxy, alkylcarbonyl or alkoxycarbonyl groups, wherein one or more H atoms may be substituted by F or Cl, Sp¹ is a spacer group comprising 1, 3 or 5 to 40 C atoms, wherein one or more non-adjacent and non-terminal CH₂ groups may also be replaced by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O—, —CH(halogen)-, —CH(CN)—, —CH═CH— or —C≡C—, however in such a way that no two O-atoms are adjacent to one another, no two —CH═CH— groups are adjacent to each other and no two groups selected from —O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O— and —CH═CH— are adjacent to each other, X¹¹ and X¹² are independently from one another a linking group selected from —CO—, —CO—O—, —O—CO—, —O—, —CH═CH—, —C≡C—, —CO—S—, —S—CO—, —CS—S—, —S—, —CF₂—, —CF₂—O—, —O—CF₂—and a single bond, however under the condition that X¹¹and X¹² are not both —O— and under the condition that X¹¹ and X¹² are both not a single bond, and under the condition that in —X¹¹-Sp¹—X¹²— no two O-atoms are adjacent to one another, no two —CH═CH— groups are adjacent to each other and no two groups selected from —O—CO—, —S—CO—, —O—CO—O—, —CO—S—, —CO—O—, —CF₂—O—, —O—CF₂— and —CH═CH— are adjacent to each other.
 2. Bimesogenic compounds according to claim 1, characterized in that at least one of MG¹¹ and MG¹² comprises one fused ring structure, two or more fused ring structures, at least part of which fused ring structure or fused ring structures is aromatic.
 3. Bimesogenic compounds according to claim 1, characterized in that both MG¹¹ and MG¹² comprise one, two or more ring structures.
 4. Bimesogenic compounds according to claim 1, characterized in that R¹² is selected from OCF₃, CF₃, F, Cl, CN and NO₂.
 5. Bimesogenic compounds according to claim 1, characterized in that Sp¹ is —(CH₂)_(o)— and o is 1, 3 or an integer from 5 to
 15. 6. A method which comprises including one or more bimesogenic compounds according to claim 1 in a liquid crystalline medium.
 7. Liquid-crystalline medium, characterised in that it comprises one or more bimesogenic compounds according to claim
 1. 8. Liquid-crystalline medium according to claim 7, characterised in that it additionally comprises one or more compounds selected from the group of the compounds of the formulae III R³¹-MG³¹-X³¹-Sp³-X³²-MG³²-R³²  III wherein R³¹ and R³² are each independently H, F, Cl, CN, NCS or a straight-chain or branched alkyl group with 1 to 25 C atoms which may be unsubstituted, mono-or polysubstituted by halogen or CN, wherein one or more non-adjacent CH₂ groups may be replaced, in each case independently from one another, by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —O—CO—O—, —S—CO—, —CO—S—, —CH═CH—, —CH═CF—, —CF═CF— or —C≡C— in such a manner that oxygen atoms are not linked directly to one another, MG³¹ and MG³² are each independently a mesogenic group, Sp³ is a spacer group comprising 5 to 40 C atoms, wherein one or more non-adjacent CH₂ groups may also be replaced by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O—, —CH(halogen)-, —CH(CN)—, —CH═CH— or —C≡C—, and X³¹ and X³² are each independently —O—, —S—, —CO—, —COO—, —OCO—, —O—CO—O—, —CO—NH—, —NH—CO—, —CH₂CH₂—, —OCH₂—, —CH₂O—, —SCH₂—, —CH₂S—, —CH═CH—, —CH═CH—COO—, —OCO—CH═CH—, —C≡C— or a single bond, and with the condition that compounds of formula I are excluded.
 9. A method comprising including a liquid crystal medium according to claim 7, in a liquid crystal device.
 10. Liquid crystal device comprising a liquid crystalline medium comprising two or more components, one or more of which is a bimesogenic compound of formula I according to claim
 1. 11. Liquid crystal device according to claim 10, characterized in that it is a flexoelectric device. 